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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 aims to assess the hybridization effect on the perforation threshold of Low-Velocity Impact (LVI) in thermoplastic glass composite laminates, incorporating layers of resin-impregnated stainless-steel mesh. Reinforcing methodologies such as hybridization are recently being adopted as a practical approach to increasing the energy-absorbing capacity of polymer composites. In the current paper, a multi-step hot press lamination method has been employed to fabricate the hybrid composite laminates strengthened with stainless-steel mesh layers. Several stacking sequences, metal mesh wire sizes, orientation and position relative to the impactor have been examined under various LVI energies. It was revealed that the LVI penetration energy was increased for the thermoplastic-based composite laminates reinforced with stainless-steel mesh layers. Furthermore, the LVI penetration energy threshold was significantly influenced by the metal mesh wire size, orientation and stacking sequence. Finally, the backlight method capability was assessed to detect the after-impact interlaminar damages. [ABSTRACT FROM AUTHOR]

A single-layer and double-layer corrugated core sandwich structure consisting of carbon fibre–reinforced polymer (CFRP) panels and aluminium alloy core layers was designed. Numerical simulations were carried out in HyperMesh/LsDyna, and the simulation results of single-layer and double-layer corrugated sandwich structure were compared with the experimental results to verify the reliability of the proposed numerical model. Compared with the results of single-layer and double-layer corrugated sandwich structure, the superiority of a double-layer corrugated sandwich structure in anti-collision performance is verified. Considering the effects of impact energy and impact position on impact force, energy absorption capacity, and failure mode, a series of low-velocity impact finite element simulations was carried out. It was found that the main failure mode of composite laminates included fibre damage, matrix damage and delamination, and core buckling. At the same impact position, the higher the impact energy, the greater the initial slopes of the contact force-time and absorbed energy-time curves, the higher the peak force, and the larger the energy absorption capacity. Under the same impact energy, when the impactor hit the wave crest of the sandwich structure, the damage to the structure was small; however, the maximum impact force on the structure was large (∼8 kN). [ABSTRACT FROM AUTHOR]

This study compares the impact damage response and self-healing potential of unstitched and stitched glass/polypropylene (PP) fiber reinforced thermoset composite structures. The novelty of this study is weaving preforms with an intra-ply hybridization of glass and thermoplastic PP fibers and stitching these preforms with a unique stitching pattern by considering the effect of stitching fiber types (PP, Kevlar®, Dyneema®, carbon and silk) on impact damage response and self-healing potential of composites. The mechanical properties of the stitching fiber influenced the composite's behavior against impact and compressive loads. The unstitched composite deflected more than stitched composites under the same impact energy levels due to delaying of delamination via stitching process. The stitching process reduced the damage areas of composites subjected to 30 J and 60 J impact energies by 57 and 86%, respectively. Structural healing significantly decreased the damaged areas of both unstitched and stitched composite structures up to 87%, while it was more effective on stitched composites. The polypropylene melted and accumulated along the path of the stitch pattern, regardless of whether the stitching fiber was thermoplastic. Due to the reduced impacted area, compression after impact (CAI) strength retention of the stitched composite materials increased by up to 94%. [ABSTRACT FROM AUTHOR]

In this study, oil palm empty fruit bunch (OPEFB)-reinforced composites were subjected to a low-velocity impact test to study their energy absorption characteristics. Two sets of OPEFB-reinforced composite specimens were used, comprising 30:70 and 40:60 fiber/epoxy fractions. One set of specimens was treated with a 3% NaOH solution. The drop impact responses, fragmentation characteristics, energy absorptions, and residual strengths of both sets of specimens were analyzed. Drop impact tests were performed using three different energy levels, namely, 10, 13, and 16 J. In general, the results indicated that all the untreated specimens absorbed higher energy than that of the treated specimens, thus suffering severe surface and structural damage. This result is attributed to the treated specimens providing a better interlocking mechanism between the matrix and fibers and dissipating the impact energy through the impactor. Regarding fiber loading, all the 30:70 fiber/epoxy composites exhibited slightly less energy absorption than the 40:60 fiber/epoxy composites. [ABSTRACT FROM AUTHOR]

In high-velocity projectile impacts, the contact duration is very short and the response of the target is governed by the local behavior of the material in the impact zone. On impact, a compressive stress wave is generated in the target, which travels in the thickness direction. This compressive stress wave plays a significant role in the failure of thick composite targets. In conventional laminates, the out-of-plane (transverse) compressive strength of composite resists the generated compressive stress wave which is not efficient since out-of-plane compressive strength is significantly lower than the fiber direction strength value. In the current numerical study, a non-conventional approach has been adopted by orienting the fibers in the impact direction to utilize the high compressive strength in the fiber direction to resist the projectile impact. In this regard, unidirectional composite rod segments are considered with fiber aligned in the projectile impact direction. The resulting effect on the impact energy absorption and the overall mechanical impact response is numerically studied and compared with conventional woven fabric laminates. Several configurations of these unidirectional fiber rod segments and the role of lateral confinement are also studied to understand their effect on the impact energy absorption. The numerical simulation results indicate an advantage for the proposed arrangement of composite (segments) rods with fiber in impact direction over the conventional woven fabric laminates. [ABSTRACT FROM AUTHOR]

As the use of composite laminates are unceasingly increasing more and more in many applications, the in-depth understanding about the impact response of composite laminates in certain areas like sport, aerospace and automotive has gained more attention of the designers and scientists over the last two decades. The authors have focused to review the impact properties of fibre reinforced composites particularly impact damage tolerance. Impact resistance, damage tolerance, composite failure and methods of assessing damage tolerance are presented. Furthermore, the approaches for improving damage tolerance such as fibre architectures resin system, and hybridisation using either yarn hybridisation or hybrid layers are discussed. In the end, a survey of modelling the impact damage of laminated composites is made by considering the inter-laminar and intra-laminar failures as key point for evaluating the response of laminates under impact loading. Graphical Abstract [ABSTRACT FROM AUTHOR]

Wheel-rail impact, which arises from structural discontinuities and short-wave defects, becomes more serious with higher train speeds and larger axle loads. The large impact load can accelerate the deterioration of vehicle-track components and induce a high level of impact noise. This paper aims to better understand the characteristics of wheel-rail impact and redevelop corresponding mitigation measures. First, a well-validated vehicle-track vertical interaction model with a singular rail defect is built up considering nonlinear Hertz contact. Then, the simulated wheel-rail impact force is characterized in both the time and frequency domains with different running speeds and defect geometries employing continuous wavelet transform. The identified characteristic frequencies are correlated to the track resonance modes. Afterward, a parameter sensitivity analysis of railpads, ballast, roadbed, and suspensions is performed to obtain the mitigation measures of wheel-rail impact. The results show that the wheel-rail impact force can be characterized by four stages in the time domain, the quasi-static stage before the impact, the forced vibration, the free vibration, and the quasi-static stage after the impact, respectively. Four characteristic frequencies are identified in the wheel-rail impact response: f 1 at 45 Hz, f 2 at 100 Hz, f 3 at 260 Hz, and f 4 at 810 Hz. Among them, f 4 has the dominant vibration energy and is determined together by the pinned-pinned resonance mode and the defect excitation frequency. Characteristic frequencies f 1, f 2, and f 3 correspond to the ballast, sleeper, and rail resonance modes, respectively, which are independent of the defect geometry. The increase of railpad stiffness can effectively reduce the maximum wheel-rail impact force and thus the impact factor. Larger railpad stiffness and damping can significantly reduce the dominant vibration energy at about 810 Hz of f 4. This work can contribute to the optimization of vehicle-track parameters for a new design of more impact-resistant railways. [ABSTRACT FROM AUTHOR]

The importance of natural reinforced bio-composite materials with desirable properties such as high modulus-to-weight ratio, good impact resistance, and the ability to be easily repaired is crucial in the industry. A woven flax/Elium® thermoplastic bio-composite is manufactured to challenge these needs. Elium® is the only resin that permits the manufacture of large parts with thermoset-like processes, as Liquid Resin Infusion presented in that work. The paper highlights the influence of stacking fibre orientation, moisture absorption, and repair aptitude on its impact resistance. An instrumented drop tower was needed to conduct low-velocity impact tests at several energies and high-speed image coupled with microscopic observations was used to assess the damage evolution. The impact resistance was improved for the dry (0/90)6 orientation, but moisture absorption decreased its impact peak force by 20%. A three-point bending test was preferred to compression after impact for studying the residual properties after impact. The bio-composites with (±45)6 orientation showed higher impact residual performance than the (0/90)6 orientation, and corresponded to the reduction of maximum bending force by 20% than that of the reference. In addition, a thermo-compression process was applied to repair the impacted plates and conduct multiple impact/repair cycles which showed a significant recovery of stiffness and maximum impact force at 4J on (0/90)6 plates, highlighting their potential for repair in the automotive and marine industries. [ABSTRACT FROM AUTHOR]

Designing bio-composites for structural applications requires a thorough understanding of their mechanical behavior. In this study, we examined the differences in the tensile strength and drop-weight impact response between polypropylene reinforced with flax fibers and that reinforced with pinewood short fibers, as both fibers differ in composition (cellulose, hemicellulose, and lignin) and length-to-diameter ratio. We found that flax fibers, which have higher cellulose content and are twice as long as pine fibers, increased the stiffness and shock resistance of bio-composite materials. However, pine fibers, which contain more lignin, showed increased material ductility and energy absorption. Impulse excitation, acoustic emission and micro-CT techniques were used to evaluate the post-impact mechanical properties and the contribution of each damage mechanism to the final material failure (tearing). The experimental results were used to validate a model based on finite elements. Our results revealed that the experimental and finite-element analyses were in good agreement. [ABSTRACT FROM AUTHOR]

Polymer matrix composites are vulnerable to low-velocity impact, although they have found many applications in high-tech industries. The main objective of this study is to improve compression after impact strength of the carbon/epoxy composites using nanoclay particles. All test samples were fabricated using a vacuum infusion process. The solution blending methodology was applied for better dispersion of the nanoparticles in the resin. The low-velocity impact response of the composite and nanocomposite laminates was investigated at various energy levels of 10, 15, and 20 J. To quantify the impact effect, the residual strength of the impacted specimens was experimentally measured under the compression test. In addition, the effect of nanoclay incorporation through the solution blending methodology on damage mechanisms was determined by the radiographic analyses and optical microscope method. The findings of this research showed a rise, up to 25.15% in the residual compressive strength, and a 7-fold increase in local buckling threshold stress of the carbon/epoxy/nanoclay specimens. [ABSTRACT FROM AUTHOR]

A novel family of composite laminates with a simplified stacking sequence and double-double layup [±ϕ/±ψ] n has significant potential to reduce weight and increase strength, while facilitating design optimization and simplifying the manufacturing process. In this study, the low-velocity impact response of a double-double (DD) laminate and a quadriaxial (Quad) laminate of equivalent stiffness and thickness were compared. Carbon/epoxy laminates were produced with stacking sequences of [±0/±50]10 and [03/90/±45/02/±45]2S corresponding to double-double and quadriaxial varieties, respectively. Low velocity impact tests were conducted at 74 J of energy and damage areas were examined using X-ray computed tomography. Compressive strength and compression after impact (CAI) strength were equivalent for the two laminates. However, differences in impact damage morphology were observed and are discussed. [ABSTRACT FROM AUTHOR]

In the present work, the low-velocity impact characteristics of the spherical core sandwich structures made of glass fibre reinforced plastic (GFRP) are tested at different strike velocities (3, 5, and 7 m/s). Four different types of core orientation, namely, regular, interlock, inverted, and stagger, are designed and fabricated by the hand-layup method. Vinyl ester resin and woven glass fibre fabrics are used as matrices and reinforcements, respectively. The diameter of the spherical core and the pitch distance is chosen as 16 mm and 32 mm, respectively. The impact behaviour of the novel spherical sandwich structures is examined based on the maximum contact force, energy absorption capacity, coefficient of restitution (COR), and damage behaviour. The Regular model shows enhanced energy absorption capacity with a specific absorbed energy of 0.092 J/(kg/m3) at 7 m/s impact velocity. Similarly the Interlock model shows good damage resistance. The typical failure patterns observed in the Interlock model at 3 m/s are matrix cracking (MC) and fibre breakage (FB), whereas, at 5 and 7 m/s impact velocities, the damage core crushing (C) is observed. [ABSTRACT FROM AUTHOR]

This study aims to investigate the low-velocity impact response of boron nitride nanoparticles (BNNPs) added carbon fiber reinforced pipes (CFRPs) at various temperature values. Carbon fiber/epoxy composite specimens with (±55°)3 winding angles were manufactured with the filament winding method. Low-velocity impact tests were performed with a 15 J energy level at five different temperatures between −196°C and 23°C ranges to understand the cryogenic environment effect on BNNP added carbon fiber reinforced tubes and neat carbon fiber reinforced tubes. The force-displacement and contact force-time graphs were attained in consequence of low-velocity impact tests. The damage areas, their size and characteristics were scrutinized both visually and with the aid of a Microscope. The test results showed that when ambiance temperatures decreased, the damage areas considerably increased both filled with BNNP and without BNNP filament wound carbon fiber reinforced tubes. [ABSTRACT FROM AUTHOR]

The Hybridization concept creates a niche within the composite segment to customize materials for specific applications with reduced cost without sacrificing strength and durability. The composite structures develop strain during continuous operation, and any sudden impact on these preloaded parts might result in catastrophic accidents. Studying impact response during such conditions is essential in designing and developing structures. This study experimentally investigates the high velocity impact response of Hybrid (Carbon-Glass) composite under normal and hydrostatic preload conditions. Mechanical tests involving Tensile, Izod, and Charpy are conducted. High velocity impact testing is carried out with a vertical single-stage gas gun with additional provision for hydrostatic preloading. An oscilloscope with a laser source measures the initial velocity, and Photogrammetry using a high-speed camera measure the residual velocity of a projectile. The mechanical test results suggest that Hybridization resulted in a significant property enhancement. The high velocity impact resistance and energy absorption are higher for Hybrid under both normal and preloaded impact. [ABSTRACT FROM AUTHOR]

The mechanisms of projectile penetration of composite sandwich panel with empty, trapezoidal corrugated cores have been experimentally investigated. The panels have been designed to investigate the influences of specific parameters, like the fiber type of corrugated core, the projectile nose shape and the stacking sequence of face-sheets, on the impact performance from the aspects of sequential deformation, failure modes and associated mechanisms. Experimental results demonstrated that usage of Twill glass fiber in corrugated core is attained highest performance in term of energy absorption and residual velocity for the fully perforated specimens. Comparisons of panels with different stacking sequences for face-sheets verify that the corrugated core composite sandwich structures with ( 0 ° ∓ 45 ° 90 ° ) s stacking sequence is indicated the highest energy absorption. This panel is displayed a superior resistance over the ones with other stacking sequences. The hemispherical projectile is showed no deviation from the direct line of path flight relative to the conical and blunt projectile in the high velocity impact test. Moreover, the deviation of the projectile decreases the damage area in specimens. [ABSTRACT FROM AUTHOR]

The low-velocity impact response of sandwich structures with aluminum face sheets and neat or nano-reinforced polypropylene core was studied. A strain-rate dependent micromechanics model (SRDM) was presented in the literature for predicting the dynamic behavior of nano-reinforced polymers. In the present study, the dynamic behavior of nano-reinforced polypropylene was simulated based on SRDM results. The finite element model was validated against the experimental results. It was shown that the results of the simulation performed by the SRDM model were in very good agreement with the experimental data. Then, the proposed finite element model was used for checking the sensitivity of the impact performance of nano-reinforced sandwich structures to the material and geometrical variations. A special sandwich structure with a core of 1 mm thickness and a face thickness of 1 mm was considered as the base structure. Different material and geometrical variations including doubling the thickness of the core or face sheets, a different weight ratio of graphene, and increasing material parameters of the face sheets up to 90%, were undertaken on the base structure. The results of the present study imply that the optimal amount of graphene should not exceed 0.5 wt.% to improve impact properties. The impact response of nano-reinforced sandwich structures was more sensitive to the variations of the face thickness in comparison to the variations of the core thickness. Moreover, the impact outputs were more sensitive to changes in the yield stress of faces compared to changes in Young's modulus of faces. [ABSTRACT FROM AUTHOR]

Composite laminates used in aircraft structures are easily subjected to multiple impacts during their service period. The detailed analysis of impact responses could reflect the stiffness of composite structure. Nevertheless, the impact response of laminates with a large width-thickness ratio is quite different from that of ordinary laminates. The deflection could reach several times the thickness during the impact. The present paper performed an experimental study using drop weight equipment to investigate the changes in dynamic mechanical behavior of carbon fiber reinforced polymer laminates during multiple low energy impacts. Three kinds of impact energy levels of 5, 10, and 15 J were applied for the single impact event. The specimens impacted at 5 and 10 J were then subjected to subsequent impacts in order to explore the differences between single and multiple strikes with the same total impact energy. The global mechanical responses during each impact procedure were recorded and analyzed by the changes of impact force, contact time, peak energy moment, energy absorption, and displacement after every single impact. Although the first strike had introduced damages into the plates, the peak force and maximum displacement increased unexpectedly rather than decreased during the second strike. Meanwhile, the damage was evaluated using ultrasonic C-scan and visual inspection. The results indicated that the multiple impacts did not produce as much damage as the first strike. Short matrix cracks were observed at the edge of the dent except for the single impact with 5 J energy. [ABSTRACT FROM AUTHOR]

Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are conducted at distinct energy levels and thicknesses to characterise the damage process. These specimens and loading conditions are representative of a new generation of critical structural components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly being made entirely from composites. The tests address the need to better understand the damage process for specimens with a small thickness ratio since existing experimental impact data for large thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric layups and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed cameras were processed in a novel way, providing the force during impact. C-scans and micrographs were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences in damage size for the thickness range analysed. The influence of layup on the global impact response is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly with the impact energy and the delaminated area linearly with the impact velocity. There is no clear correlation between the compression-after-impact failure mechanisms and the residual strength. Impact damage, at the current energy levels, showed a minimal reduction of residual strength. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer composites serving in harsh conditions must maintain their performance during their entire service. The cryogenic impact is one of the most unpredictable loading types, leading to catastrophic failures of composite structures. This study aims to examine the low-velocity impact (LVI) performance of 3D woven spacer glass-epoxy composite experimentally under cryogenic temperatures. LVI tests were conducted under various temperatures ranging from room temperature (RT) to −196°C. Experimental results reveal that the 3D composites gradually absorbed higher impact energies with decreasing temperature. Besides, the effect of multi-walled carbon nanotube and SiO2 nanofiller reinforcements of the matrix on the impact performance and the damage characteristics were further assessed. Nanofiller modification enhanced the impact resistance up to 30%, especially at RT. However, the nanofiller efficiency declined with decreasing temperature. The apparent damages were visually examined by scanning electron microscopy to address the damage formation. Significant outcomes have been achieved with the nanofiller modification regarding the new usage areas of 3D woven composites. [ABSTRACT FROM AUTHOR]

Joining dissimilar materials to achieve lightweight design and energy efficiency has been increasingly popular. A joint formed by components of particle-reinforced metal and polymer matrix composite combines the merits of both materials. This paper is mainly focused on the research of the tensile lap shear and impact behavior of the dissimilar single-lap joints (SLJs) between SiCp/AA2124 composite and glass fiber-reinforced polypropylene (PP). The effects of out-of-plane loading applied from different surfaces of SLJs on impact responses are evaluated. Hot pressing technique is introduced to manufacture metal/polymer assembly without using any adhesive. The hole drilling effect is investigated with the idea that it may provide weight reduction and also increase the strength of the dissimilar SLJs. The results indicate that the dissimilar SLJs show more Charpy impact strength when the impact is performed on the metal-matrix composite (MMC). Mechanical properties of SLJs are adversely affected by a drilled hole in the MMC adherend. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the damages of glass fiber reinforced plastic (GFRP) composite tubes under the effect of low-velocity impact (LVI) at cryogenic environment conditions and room temperature. A GFRP composite tube consists of 6 layered E-glass/epoxy samples with a ± 55° winding angle, which produced by the filament winding method. Composite tubes either at room temperature or conditioned by liquid nitrogen at different temperature values (273 K, 223 K, 173 K, and 77 K) were impacted at 5, 7.5, and 10 J. Also, force-time and force-displacement graphs were plotted. The damaged regions of the samples were scrutinized. The damage areas of the GFRP composite tubes were smaller as the temperature decreased. However, the energy absorbed at low-temperature conditions was slightly higher than that absorbed in room temperature. Besides, no micro-cracks developed in the composite tubes after cryogenic conditioning. [ABSTRACT FROM AUTHOR]

In this work a natural fiber composite material, the Guadua Angustifolia Kunth from the family of Bamboo is investigated as a suitable alternative for solutions for impact applications, load-bearing, and other structural applications. Since this type of Bamboo grows faster than wood and requires less water and area to reach maturity and be able to crop, it is a competitive, economically, and environmentally solution when is compared to other construction materials. The Bamboo species of interest is a natural one from Colombia and will be evaluated in flexural behavior and under impact response to understand the material subjected under fast loading. Flexural samples were cut parallel to bamboo axial fibers to obtain the highest impact strength. The flexural tests and scanning electron microscopy characterization were included for microstructure analysis. Additionally, compression at high strain rates was characterized by a split-Hopkinson pressure bar (SHPB). Results show flexural strength of about 70 MPa. The impact analysis showed a tough material with very similar values to Charpy notched and dynamic instrumented impact tests. [ABSTRACT FROM AUTHOR]

It is a challenging task to advance the excellent strength and structural performance of sandwich structures, while continuing to reduce the weight and cost parameters. Thousands of researchers have studied and developed the core structural innovation with periodical achievements. This review paper concentrates on the core structural trends and impact response of sandwich panels, which highlights the novel design concepts and impact failure modes. Three kinds of core structures have been classified, which are foam-core, two- and three-dimensional periodic cores. It is shown that the core structure of sandwich panels plays a vital role in structural performance and applications. Three common types of loading conditions have been considered, i.e. compression, projectile impact and three-point bending. Examples of novel core structures are further studied and summarised under corresponding impact loadings. Recent applications of sandwich structures are briefly concentrated on aerospace, automotive, marine and civil engineering areas. Furthermore, future research and development prospect of sandwich structures are suggested and predicted. [ABSTRACT FROM AUTHOR]

Improvement in mechanical properties of natural fiber reinforced polymeric composites remain a key focus of researchers in the recent years. However, few studies have been carried out for the improvement in low velocity impact properties of such composites. In the present article, the results on the effect of weave structure of reinforcing fabric and addition of glass microsphere fillers (GMS) on the drop weight impact properties of Hemp/Green epoxy composite samples are reported for the first time. Hemp woven fabrics having four different weave structures (matt, satin, hybrid weave A and hybrid weave B) were developed in an inhouse lab. Four layered composites containing glass microspheres (0%, 2%, 3.5% and 5% on the weight of resin) were fabricated using vacuum bag molding. Drop weight impact testing was performed at 10 J impact energy, and force-displacement, force-time and energy absorbed-time behaviors were recorded and analyzed. The results were statistically analyzed as well. It was found that both weave design and glass microspheres show a significant effect on impact properties of the developed composites. The composite sample reinforced with satin woven reinforcement exhibited maximum value of impact force, whereas composite samples containing 5% glass microspheres display more resilience and stiffness as compared to other structures. [ABSTRACT FROM AUTHOR]

This paper investigates the penetration and energy absorption mechanisms of ultra-high-molecular-weight polyethylene plain weaves with different fabric properties. Impact tests along with finite element (FE) analysis were used to study the impact response of the fabrics. In this research, the impacting projectile did not cause any fiber or yarn failure on the samples. It was found that structural parameters determine the yarn pull-out behavior and the softness of the resultant fabrics. Fabrics formed by loosely interlaced yarns tend to exhibit higher softness and less resistance against yarn pull-out. When the projectile velocity is not sufficient to initiate yarn pull-out, material softness determines the depth of the backface signature on the clay witness. This trend is more pronounced in a multi-ply fabric system than in a single-ply system; when yarn pull-out occurs, the projectile-slowing mechanism depends on the frictional force between the warp and weft yarns. Therefore, fabric softness becomes less important, and the yarn pull-out behavior of the fabric plays a predominant role in energy absorption. FE prediction showed that tightly woven fabrics exhibit a larger area of stress distribution and material deformation than those with severe yarn pull-out and, consequently, these tight fabrics tend to absorb more kinetic energy and sustain higher impact load from a projectile. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the low velocity impact behavior of pre-stressed glass fiber/epoxy (GRP) nanocomposite tubes. During the production of filament wound tubes with a winding angle of ±55°, carbon nanotubes (CNT) were introduced to the epoxy resin at 0.5%wt and 1.0%wt by ultrasonic method. The nanocomposite tubes were pre-stressed to 32 bars internal pressure, one of the specified operating pressures according to ANSI/AWWA C950 standards. Low velocity impact tests were performed on the pure and CNT added pre-stressed GRP tubes at 5, 10 and 15 Joule energy levels. As a result of the experiments, the contact force-time, force-displacement graphs and absorbed energy values by the samples were obtained. In addition, the damage zones on the specimens were investigated. The effects of CNT reinforcements on the impact response and damage mechanisms of the specimens were evaluated. By adding CNT, it was observed that the damage areas of the samples decreased and was found to affect the impact response of nanocomposite tubes. [ABSTRACT FROM AUTHOR]

The beneficial effect of STF impregnation in enhancing the impact resistance of high-performance fabrics has been extensively reported in the literature. However, this research work reports that fabric structure has a decisive role in moderating the effectiveness of STF impregnation in terms of impact energy absorption. Plain woven fabrics having sett varying from 25 × 25 inch−1 to 55 × 55 inch−1 were impregnated with STF at two different padding pressures to obtain different add-ons. The impact energy absorption by STF impregnated loosely woven fabrics was found to be higher than that of their neat counterparts for both levels of add-on, while opposite trend was observed in case of tightly woven fabrics. Further, comparison of tightly woven plain, 2/2 twill, 3/1 twill and 2 × 2 matt fabrics revealed beneficial effect of STF impregnation, except for the plain woven fabric, establishing that there exists a fabric structure-STF impregnation interplay that tunes the impact resistance of woven fabrics. [ABSTRACT FROM AUTHOR]

Based on economic and environmental factors related to energy efficiency, the automotive industry is being increasingly encouraged to design lighter structures, making use of adhesive bonding in vehicle body frames. To meet the standards of the automotive sector, adhesive joints must provide high strength and stiffness, low cost and good energy absorption at a component level, thereby ensuring good impact strength and passenger safety. This work aims to study, at room temperature (24°C), the impact response of a real scale automotive structure bonded with a crash-resistant epoxy, allowing to access the suitability of adhesives for automotive structural purposes. The epoxy adhesive was found to successfully transfer the loads to the aluminium substrates and not to compromise the integrity of the structure, as its failure was dominated by the behaviour of aluminium. Results obtained with a numerical model of the component were found to be in close agreement with the experimental failure load, demonstrating that numerical analysis can be a viable tool to predict the structure's behaviour. In addition, a polyurethane was used as an alternative to the epoxy system to bond the structure, proving that the joint behaves better in the presence of a more flexible adhesive, as no failure was found for this case. Aluminium single-lap joints with two adhesive thicknesses were tested as a complement to understand the influence of this parameter on the impact response of a joint, showing a 21% decrease in strength when the highest thickness was used. [ABSTRACT FROM AUTHOR]

In this study, the mechanical behavior of sandwich plates with functionally graded core under low-velocity impact loads was investigated experimentally. Sandwich plate with functionally graded core has two different structures (metal–ceramic), and the upper and lower surfaces are pure metal (Al) and the internal layers of the plate are manufactured with gradually varying material composition through the plate thickness. The low-velocity impact tests were conducted on both upper and lower surfaces of specimens using CEAST low-velocity impact device, and the contact force–time and the energy–time graphs were plotted. Metallographic and micromechanical examinations were carried out on the specimens after impact tests. As a result of the metallographic and micromechanical examinations, the material composition variation through the specimen thickness was obtained in accordance with the rule of the theoretical mixture. As a result of impact tests (v = 4 m/s) on upper surface (ceramic-rich side), crack damages occurs on the plates with n = 10.0 material composition, whereas the specimens with n = 1.0 and n = 10.0 material compositions have crack damages after impact tests on its lower surfaces (metal-rich side). Impact force on the ceramic-rich upper surface provides to meet the transferred load waves through the plate thickness by metal-rich bottom surface. This situation makes the structure more resistant against damage. Moreover, the upper and lower surfaces of the functionally graded structure reinforced by ductile pure metal layers provide an important contribution to protection of functional integrity of the structure against damage. [ABSTRACT FROM AUTHOR]

The year 2019 marks the anniversary of two major US offshore oil spills: the 50th anniversary of the Santa Barbara spill and the 30th anniversary of the Exxon Valdez. The consequences of these spills are profound, echoing throughout countless environmental, ecological and social systems. Each spill sparked a flurry of research focusing on the analysis and documentation of spill impacts and responses. The purpose of this progress report is to evaluate oil spill modeling research as a knowledge domain. Using bibliometric analysis techniques, we constructed a co-citation network for exploring key areas of research and seminal papers to highlight the evolution of oil spill research over the past 50 years. The paper concludes with recommendations for future work, detailing the importance of connecting the physical and social sciences for deepening our understanding of oil spills and their broader implications for communities and the environment. [ABSTRACT FROM AUTHOR]

Fiber metal laminates are commonly used materials in industrial applications due to low density and excellent mechanical properties such as impact resistance. In this study, the effect of shape memory alloy wires on the impact properties of fiber metal laminates is evaluated and discussed. The volume fraction of wires and the pre-strain of wires were selected as the variables of the experiments. The samples were fabricated using hand lay-up method and their behavior was evaluated under high-velocity impact test. Based on the results, a significant change in the amount of absorbed energy was obtained using embedded wires. However, with increasing the volume fraction of wires, the absorbed energy decreases due to the discontinuity in mechanical properties of the specimens. On the other hand, applying pre-strain leads to residual stresses in samples. The observed residual stress in specimens with four embedded wires and 2% pre-strain level shows the most absorbed energy. [ABSTRACT FROM AUTHOR]

In the current study, the low-velocity impact response of hybrid-laminated composites based on the twill woven fabrics was investigated experimentally. The following five different types of carbon–aramid/epoxy hybrid laminates were produced and tested, (a) two types of interply hybrid, (b) two types of sandwich-like interply hybrid, and (c) intraply hybrid. Non-hybrid carbon and aramid twill woven laminates were also tested for comparison. The effects of the hybrid structure on the impact properties such as the peak load, the ductility index, and damage area were discussed. The impact damage resistances of specimens were evaluated by comparing damage images taken from both the impacted and the non-impacted surface. The damage and failure mechanisms were analyzed from the impact damage morphologies using ultrasonic C-scan and three-coordinate measuring device. Under the same impact energies, the interply hybrid laminates with carbon fabric on the impact surface have higher impact damage resistance. It can be concluded that placing of high stiffness carbon fabric at highly stressed regions as reinforcement would result in enhanced properties, and the damage tolerance performance of composites with interply hybrid structure are better than those of other hybrid composites. [ABSTRACT FROM AUTHOR]

This article deals with the dynamic response of thin circular clamped GLARE (GLAss REinforced) fiber-metal laminates subjected to low-velocity impact by a lateral hemispherical impactor, striking at the center with constant kinetic energy. The laminates have equal total thickness and consist of GLARE 2A-3/2-0.4, GLARE 2A-4/3-0.238, GLARE 3-3/2-0.4, GLARE 4-3/2-0.317, and GLARE 5-3/2-0.233 standard grades. Three different plate diameters are considered for each GLARE grade. Their dynamic response is predicted by solving previously published differential equations of motion corresponding to a spring-mass modeling of the impact phenomenon. The obtained results are analyzed and compared in order to understand and evaluate the performance of the examined material grades along with the effect of different plate radius. With reference to the radius variation, it is found that it affects substantially the overall impact behavior of a GLARE plate. As far as the examined material grades are concerned, similarities and differences related with their impact behavior are recorded and a comparative evaluation is implemented. Characteristic variables associated with the low-velocity impact response of fiber-metal laminates are discussed and pertinent design recommendations are proposed. [ABSTRACT FROM AUTHOR]

A global–local methodology is presented for predicting the response of sandwich composite plates with piezoelectric transducers to low-velocity impact. Model reduction techniques have been employed in order to build a computationally efficient plate-impactor structural system, solution of which yields the global plate’s response. Higher-order layerwise kinematic assumptions enable estimation of the stress distribution locally through the thickness of the laminate and prediction of stress at the interface between different materials. Using the developed method, impact identification studies have been conducted in order to estimate impact location and impactor mass and velocity, and to reconstruct the impact event, including impact force history, posteriori. In order to validate the developed methodology, a low-cost portable experimental configuration for impact testing has been designed and impact measurements were compared to the predictions. [ABSTRACT FROM AUTHOR]

This part presents a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics under various loading conditions using quasi-static compressive stress–strain data. The model was established based on a nonlinear mass-spring-damper system by considering spacer yarns as nonlinear springs with damping effect and representation of their stiffness by the constitutive model developed in Part I. Based on the dynamic model, the impact compressive responses of a typical warp-knitted spacer fabric was parametrically studied in terms of damping ratio, initial velocity, striker mass and contact area. The study indicates that damping can reduce the peak acceleration and peak displacement regardless of loading conditions, and the increase of the initial velocity can enhance the damping effect. Increasing initial velocity or striker mass while keeping the counterpart constant can increase the peak acceleration and peak displacement. However, at a constant kinetic energy, either increasing striker mass or decreasing initial velocity can reduce the peak acceleration, but the peak displacement keeps constant. The study also shows that an optimal size of the spacer fabric exists for achieving minimal peak acceleration under impact at a certain kinetic energy. Experimental validation by drop-weight impact tests demonstrates that the predictions of the dynamic model are in satisfactory agreement with the experimental results. Using the quasi-static compressive data from a simple test, this dynamic model can numerically simulate the full time-response of warp-knitted spacer fabrics under various impact conditions. [ABSTRACT FROM AUTHOR]

This paper presents the effect of oblique impact angle on low velocity transient dynamic responses of delaminated composite pretwisted shallow conical shells. An eight-noded isoparametric quadratic plate bending element is employed in the finite element formulation incorporating rotary inertia and effects of transverse shear deformation based on Mindlin’s theory. The modified Hertzian contact law which accounts for permanent indentation is utilized to compute the contact force, and the time-dependent equations are solved by Newmark’s time integration scheme. A comparative study is carried out on torsion stiff, cross-ply, and bending stiff laminates to investigate the effects of triggering parameters like angle of twist, plate displacement, striker’s velocity, and displacement for graphite-epoxy composite laminate subjected to low velocity oblique impact at the center. [ABSTRACT FROM AUTHOR]

Low-velocity impact tests have been conducted on sandwich beams and panels based on [0°, 90°] glass fibre-reinforced epoxy skins with an aluminium honeycomb core. The sandwich beams were placed on simple supports positioned at different separations to investigate the effect of target size on their impact response. Two thicknesses (13 and 26 mm) of honeycomb core were investigated. Following impact, damage within the beams was assessed by sectioning the samples and observing them under a low-power microscope. An energy-balance model was used to predict the maximum impact force for subsequent comparison with the experimental results. The energy-balance model was used to partition the energy absorbed during the impact event, giving an understanding of the energy absorption process. Finally, a limited number of tests have been conducted on square sandwich panels in order to investigate the effect of impact loading on their indentation behaviour. An examination of the cross-sections of impacted samples highlighted regions of core buckling and local plastic folding. At higher energies, damage in the form of localized fibre fracture was observed in the top skin close to the point of impact. The energy-balance model predicted the elastic response of the sandwich beams with reasonable success. The accuracy of the model decreased as damage became more extensive in the beams. It has been shown that the level of permanent indentation in both the beams and the square panels collapsed onto a single curve when the data are plotted against maximum impact force. [ABSTRACT FROM AUTHOR]

This study investigates the performance of particulate-filled thermoplastic fluoropolymer coatings under both dynamic impact tests and static indentation tests. An instrumented impact testing rig was used to measure the impact energy, impact velocity, acceleration and impact force during the impact tests. Coating samples with different thicknesses of coating layers and steel substrate were impact tested to investigate the effect of coating and substrate thickness on the impact response and damage to the coatings. The data obtained from the dynamic tests were used to calculate the Meyer hardness values of the coating and compared with the Meyer hardness results obtained from Brinell indentation tests on the coating. The Meyer index m was similar under dynamic impact and static indentation testing conditions. The Meyer hardness calculated from the impact tests does not change markedly as a function of depth of penetration normalised to the thickness of coating, whereas the Brinell hardness increases with the depth of penetration to coating thickness ratio. For a given value of indentation strain, the Meyer hardness calculated from the maximum force measured in the impact test is approximately 2.5 times that resulting from the Brinell test. This reflects the fact that the higher strain rate in the impact test would give rise to a higher flow stress and thus hardness. [ABSTRACT FROM PUBLISHER]

A series of ballistic tests on triaxial braided carbon/epoxy composites were described in Part I of this paper. In this part, numerical simulations were carried out to investigate the impact response, damage evolution, and penetration mechanisms of these composites. A continuum finite element model was developed to obtain the time history of the projectile velocity, displacement, penetration resistance force, and energy absorption during the impact process. By fitting the numerical data, the ballistic limit velocity can be obtained. Good agreements were achieved between numerical results and experimental results. Numerical predictions for ballistic tests of the composites indicate that, based on variations of damage mechanisms and failure features, the impact process can be subdivided into three stages, i.e. phase I – shock compression, phase II – bulge deformation, and phase III – penetration process, among which phase II consumes most of the projectile kinetic energy. The differences between a blade-like projectile and a cylindrical projectile in the impact process are also addressed in detail. [ABSTRACT FROM PUBLISHER]

To investigate the high-velocity impact response and damage evolution of the triaxial braided composite fan case, a series of ballistic impact tests using blade-like projectiles were conducted. Cylindrical projectiles of the same cross-section perimeter were also employed to identify the influence of projectile geometry. In addition, satin woven composites were tested for comparison with respect to failure modes and damage shape. Experimental results indicate that the main failure modes for the two different fiber reinforcement architectures are similar, that is, fiber shear failure and matrix crush failure in the impact surface and fiber tensile failure, fiber pull-out, matrix cracking, and delamination in the exit surface. The damage area in the exit surface is diamond-shaped for satin woven composites while rounded or elliptic for triaxial braided composites according to projectile geometry. The triaxial braided composites have an improved ballistic resistance and higher ballistic limit than satin woven composites. Based on damage area and failure modes observed from experiments, ballistic behavior was predicted using an analytical model, which proves to be accurate enough. [ABSTRACT FROM PUBLISHER]

Present work intends to study the improvement of impact performance on sandwich composites by the addition of nanoclays. For this purpose, nanoclays Cloisite 30B were previously subjected to a silane treatment in order to improve their dispersion and interface adhesion. Different incident impact energy levels were used and, for both sandwiches, the maximum load, displacement or elastic recuperation shows to be very dependent of the impact energy. Mathematical relationships are proposed to estimate the maximum impact force and displacement, based on the total impact energy and impact bending stiffness. Finally, sandwiches enhanced by nanoclays presented higher maximum impact loads, lower displacements, the best performance in terms of elastic recuperation and maximum residual flexural strength. [ABSTRACT FROM AUTHOR]

The high-velocity impact response of fibre metal laminates based on a woven polypropylene fibre reinforced polypropylene, termed a self-reinforced polypropylene, and a glass reinforced polypropylene has been investigated. Two types of aluminium alloy were considered, these being the 2024-O and 2024-T3 alloys. Tests on these composite–metal hybrids were undertaken using a gas gun over a wide range of incident impact energies. In this study, attention focused specifically on the perforation threshold. Following impact, the fracture mechanisms in the two types of fibre metal laminates were elucidated by sectioning and polishing samples through the point of impact and also by measuring the residual deformation of the hybrid plates. Cross-sections of the failed samples highlighted significant plasticity within the volume of these hybrid materials, indicating that considerable energy had been absorbed in plastically deforming the aluminium and composite plies. The impact resistances of the various laminates were compared by determining their specific perforation energies. Here, it was shown that fibre metal laminates based on the glass reinforced polypropylene composite offer a slightly higher perforation resistance than the self-reinforced polypropylene fibre metal laminates. Also, the fibre metal laminates based on the stronger 2024-T3 alloy out-performed their 2024-O counterparts. Finally, the perforation resistances of the fibre metal laminates were predicted using the previously reported Reid–Wen impact perforation model. Good agreement was observed between this impact model and the measured experimental data. [ABSTRACT FROM PUBLISHER]

Use of laminated composite in the different weight-sensitive branches of engineering has gained immense popularity due to its high stiffness-to-weight ratio. In spite of this great advantage, this material is vulnerable to damage under impact loading due to its low transverse shear strength. A look through the literature on shell reveals that the impact response of civil engineering shell structures has not received proper attention. This article aims to carry out such a study of composite civil engineering shell considering skewed hypar as the geometric configuration. The modified Hertzian contact law which accounts for the permanent indentations is utilized to compute the contact force and the time-dependent equations are solved by Newmark’s time integration algorithm. Parametric studies are performed for the centrally impacted cross and angle ply skewed hypar shells modeled with eight noded isoparametric doubly curved shell elements. Simply supported boundary condition and different impact velocities are considered. [ABSTRACT FROM AUTHOR]

The low-velocity impact response of a series of glass fiber reinforced epoxy/aluminum alloy fiber metal laminates has been investigated. The influence of varying target thickness, plate diameter, and impactor radius has been studied and the results compared to those offered by plain composite samples. After testing, many samples were sectioned in order to highlight the failure modes under low-velocity impact loading. The FMLs absorbed significant energy in plastic deformation, tearing the metal layers and fiber fracture, and offered a superior impact resistance to the plain composite on which the FMLs were based. The perforation data were normalized by the areal density of the target and the superiority of the metal—composite hybrids remained in evidence. Increasing the target size, the plate thickness, and the indentor diameter resulted in an increase in the energy required to perforate the target. In contrast, impacting the square panels at the corner or along the edge of the target did not have a significant effect on the perforation response of the structures. [ABSTRACT FROM AUTHOR]

Scaling effects in the low velocity impact response of a polypropylene-based fiber-metal laminate (FML) structure have been investigated. The FML was based on a 2024 aluminum alloy, a self-reinforced polypropylene composite and a polypropylene film acting as an interlayer adhesive. The study focuses on the assessing the possibility of using scale model tests for predicting the full scale low velocity impact response of FMLs based on [Aln, 0°/90°n]s and [A1, 0°/90°]ns configurations. These two systems were used to scale four different sample sizes (n = 1/4, 1/2, 3/4 and full scale). The impact load-displacement traces were normalized and found to collapse onto a single curve, suggesting that the laminates obey a scaling law. Attention also focused on characterizing the resulting damage in these multi-layered systems, where it was shown that the deformation modes and failure mechanisms were similar in all four scaled sizes. Other parameters such as the maximum impact force and the time to maximum load showed little sensitivity to scale size. This evidence suggests that data collected from tests on small FML plates can be used to predict the low velocity impact response of larger, more representative structures. [ABSTRACT FROM AUTHOR]

The capabilities for monitoring impact forces on an aircraft composite wing using impact response function (IRF) are examined. The IRF is derived based on the finite element method (FEM). Impact locations are identified by minimizing strain errors and force deviation errors. The reconstruction of impact forces are performed by computational inverse methods. The results of impact location identifications and impact force reconstructions are verified by numerical simulations using finite element analysis. [ABSTRACT FROM AUTHOR]

This paper presents experimental investigations on impact response of fiberglassaluminum (FGA) composites. A number of test specimens were subjected to increasing impact energies until complete perforation of the target was achieved. The damage process of fiber-glass aluminum (FGA) composites is examined by comparing the load-deflection curves, energy profile diagram (showing the correlation between impact energy and absorbed energy) and images of damaged specimens. The failure processes in the impact-loaded FGAs were initially investigated by examining the front and rear surfaces of the damaged samples. After initial examination, damage mechanisms at the interior layers were ascertained through destructive analysis, i.e., sectioning and de-plying, of samples. Careful examination of the damaged FGA panels highlighted a number of failure mechanisms such as permanent plastic deformation, tearing and shear fracture in the aluminum layers as well as fiber fracture in glass-epoxy layers, and delamination between adjacent layers, i.e., at composite/composite and composite/metal interfaces. Along with the cross-sections, images of several impacted samples for varied impact energies are provided for discussion. [ABSTRACT FROM AUTHOR]

In the present study, Nanomer® I-28E, organically modified montmorillonite nanoclay supplied by Nanocor Inc., was used to modify SC-15, a toughened epoxy system using sonication route. Different weight percentage ranging from 1-3% of nanoclay was used. The modified epoxy was then used to fabricate 15-layer plain weave carbon/epoxy composite laminates using a vacuum assisted resin transfer molding (VARTM) method. Samples of size 100 x 100 mm were cut from the laminates and were subjected to low-velocity impact loading using an instrumented drop-weight system (Dynatup Model 8210) at three different energy levels of 10, 20 and 30J. Transient response of the samples was recorded and analyzed in terms to load-energy vs time relations. Impact damage was characterized by utilizing an ultrasonic nondestructive evaluation system (c-scan). Results of the study indicate that the infusion of nanoclay in the system reduced the impact damage though the impact response in terms of the peak load remained mostly unaltered. Reduced damage size was attributed to increased stiffness and resistance to damage progression of the nanophased laminates. [ABSTRACT FROM AUTHOR]

The impact response and the impact-induced damage in a curved composite laminate subjected to transverse impact by a metallic impactor are studied using a three-dimensional finite element method. Several example problems of a graphite/epoxy cylindrical shell are considered and effects of impactor parameter (impactor velocity and impactor mass) and laminate characteristics (shell curvature and fiber orientation of plies) are established. Impact-induced damages (matrix cracking and delamination) are predicted using appropriate three-dimensional stress-based failure criteria. In order to take account of degradation of material due to damage during the impact, the stiffness matrix of the failed region of the laminate is reduced as the solution progresses. [ABSTRACT FROM AUTHOR]