Low-velocity impact behavior of abaca/epoxy composites with layer variations

Due to their excellent performance, composite materials are increasingly used in the marine field. It is of great importance to study the low-velocity impact performance of composite laminates to ensure the operational safety of composite ship structures. Herein, low-velocity drop-weight impact tests were carried out on 12 types of GRP laminates with different layup forms. The impact-induced mechanical response characteristics of the GRP laminates were obtained. Based on the damage model and stiffness degradation criterion of the composite laminates, a low-velocity impact simulation model was proposed by writing a VUMAT subroutine and using the 3D Hashin failure criterion and the cohesive zone model. The fibre failure, matrix failure and interlaminar failure of the composite structures could be determined by this model. The predicted mechanical behaviours of the composite laminates with different layup forms were verified through comparisons with the impact test results, which revealed that the simulation model can well characterise the low-velocity impact process of the composite laminates. According to the damage morphologies of the impact and back sides, the influence of the different layup forms on the low-velocity impact damage of the GRP laminates was summarised. The layup form had great effects on the damage of the composite laminates. Especially, the outer 2‒3 layers play a major role in the damage of the impact and the back side. For the same impact energy, the damage areas are larger for the back side than for the impact side, and there is a corresponding layup form to minimise the damage area. Through analyses of the time response relationships of impact force, impactor displacement, rebound velocity and absorbed energy, a better layup form of GRP laminates was obtained. Among the 12 plates, the maximum impact force, absorbed energy and damage area of the plate P4 are the smallest, and it has better impact resistance than the others, and can be more in line with the requirements of composite ships. It is beneficial to study the low-velocity impact performance of composite ship structures.

The development of the composite materials in the past decades has made the composite materials more and more widely used in various engineering fields. The mechanical properties of the composite materials are gradually improved, especially the impact resistance. In this article, the damage of carbon fiber foam sandwich structure (material grade: W-3021FF/H60) under different sandwich thicknesses and impact energies was studied. Ultrasonic C-scan was used to measure the depth and area of impact damage area. Finally, the impact energy and foam core thickness on impact damage was analyzed by test results. The results show that the impact damage depth and area of foam sandwich structure were positively related to the impact energy, and with the increase in the impact energy, the growth rate of damage depth and damage area changes; the greater the thickness of the foam core was, the stronger the span-direction guiding energy for impact energy, the larger the damage area and the smaller the damage depth. Under the same energy, the more the layers of carbon fiber cloth with the foam sandwich structure, the larger the impact damage depth and the smaller the impact damage area. The proportion of ±45° ply in the foam sandwich structure can improve its impact resistance.

The need for quasi-static indentation test method for modeling low-velocity foreign object impact events would prove to be very beneficial to researchers. In order to examine whether it is feasible, series of quasi-static indentation and low-velocity impact tests were carried out and compared. An analysis of the relationships between impact energy (or quasi-static indentation force) and damage area, dent depth indicates clearly that dent depth was selected as the damage parameter to set up damage relationship between the two tests. The knee points of dent depth appearing in the two tests curves were very close. The variation tendency of the dent depth, the process curves and the cross sectional damage views of the two tests were in similarity. Results show that no distinct differences could be seen between low-velocity impact and quasi-static indentation testing, indicating that quasi-static indentation testing can be used to represent low-velocity impact testing.

ABSTRACTThe low-velocity impact studies to account for the variation in the number of basalt fiber layers in the through-thickness loading performance of natural fibre reinforced polymer composites are very limited. These studies are useful to understand the external and internal failure mechanisms of composites at different thicknesses. In this study, the single and multilayered basalt/polyester composite samples were fabricated, as the number of basalt fibre layers increased gradually from 1 to 9, and then low-velocity impact tests were conducted at a constant impact energy of 12 J. The impact data was measured using the LabVIEW software. Further, full-field failure or damage mechanisms of composite samples were investigated using ultrasonic A, B and C scan techniques. Failure mechanisms observed in tested samples were matrix cracking, fibre breakage, delamination, etc. However, the size and shape of failure mechanisms observed were varying with the increase in the number of layers. Samples that had a smaller number of basalt fibre layers (1–4) failed rapidly due to extensive regions of delamination and the failure mode observed was localised damage with higher regions of delamination. However, samples that had a greater number of basalt fibre layers (5–9) could withstand higher impact loads and failed progressively. The failure mode observed in these samples was mainly distributed damage with lower regions of delamination.

The objective of this study was to assess the influence of fibre orientation in hybrid fibre metal laminates based on aluminium and carbon fibres on the impact of low-velocity impact. The analysis was conducted on the basis of fibre metal laminate impact resistance criteria, including impact force, energy absorption, bending stiffness, damage area and failure. To assess the resistance of various aluminium–carbon laminates, qualitative and quantitative evaluation criteria were employed, including the shape of the force–time curve, characteristic impact forces, energy absorption, bending stiffness, damage area and external failure analysis. Among others, authors concluded that no explicit influence of the composite layer fibre orientation on the shape and value of characteristic forces was observed. It was found that the fibre orientation and the changing number of interfaces of low durability show no explicit influence on the size and shape of delaminations.

In this study, the behavior of 2D and 3D woven composites is compared under low velocity impact. Several 2D and 3D specimens were tested using a drop-weight tower, and their performance was compared using extracted data such as damage threshold load, damage initiation time, absorbed energy and maximum deflection. Besides, their damage modes and delamination areas were examined by stereomicroscope and C-scan technique, respectively. The results showed that the 3D woven composites absorbed more impact energy than 2D ones while their maximum deflection was lower. Moreover, the delamination and damage areas were much smaller in the 3D composites than the 2D ones of similar thickness. A new parameter is presented for comparing damage severity of the 2D and 3D composites. Unlike conventional parameters, the presented one shows potential for being applicable to laminated composites, regardless of their areal densities, layer numbers and weave structures.

Protective structures subjected to intensive loads that may benefit from the use of multilayer composite structures with excellent hardness and impact resistance represent an emerging research field in recent times. In this study, low-velocity projectile impact tests were performed on Functionally-graded Preplaced Aggregate Fibrous Concrete (FPAFC) mixtures to evaluate their performance. The effects of projectile needle type, fibre type and hybridization in addition to the number of layers in the composites on projectile impact were investigated. The bioinspiration of the excellent impact strength of turtle shells was used to design an FPAFC comprising a higher amount of steel and polypropylene fibres at the outer layers. In parallel, one and two-layered concretes were also cast to assess the effectiveness of three-layered FPAFC. The tests were performed on disc specimens using non-deformable compound bevel, convex edge and hollow edge projectiles. The damage severity was quantified by the top damage area, bottom damage area and depth of penetration. In addition, a simple analytical model for predicting the composite mass expulsion was developed and implemented. Findings indicated that regardless of fiber type and distribution, the compound bevel projectile needle produced the lowest impact numbers for all single, double and triple-layer specimens compared to the convex edge and hollow edge projectiles. Repeated projectile impacts increased the penetration depth and damaged area at the top and bottom surfaces of all targets. Targets were more resistant to convex edge and hollow edge projectile penetration than the compound bevel. The experimental and analytical model results for mass expelled from the top surface are reasonably acceptable. This research gives an idea of developing advanced fibrous composite with superior impact resistance for the promising protective structures.

Plain glass fibre-reinforced polymeric (GFRP) laminates and GFRP reinforced with randomly oriented short strips of shape memory alloy (SMA) were prepared by hand lay-up method. The SMA strip reinforcement was placed at 0.75 × thickness of the laminate with weight fractions of 2, 4 and 6%. The specimens were exposed to drop weight impact test and the experiments were conducted at a constant impact velocity of 2.80 m s−1 with different test temperatures such as 303, 333 and 363 K. The impact damage area was evaluated using lighting technique and fracture response was analysed using scanning electron microscopic (SEM) images. Absorption of impact energy and damage area due to low velocity impact were calculated. It was observed that with the higher temperature, the SMA/GFRP laminates exhibit marginally-enhanced damage resistance compared to the plain GFRP laminates. Also, addition of SMA reinforcement was not contributing much to the impact resistance at higher temperature.

Carbon fiber-reinforced Aluminum Laminate (CARALL) is a new generation of Fibre Metal Laminate (FML) material. This study investigates the low-velocity impact behavior of CARALL structures at different environmental temperatures (−40°C, 23°C, and 80°C). Two different groups of CARALL composite structures with varying fiber orientations were produced by hot pressing in a 3/2 arrangement: C1 (Al/0°90°/Al/90°0°/Al) and C2 (Al/0°0°/Al/0°0°/Al). Low-velocity impact tests were conducted at 23 J, 33 J, and 48 J energy levels using a Ø20 mm spherical impactor tip. The area of damage was detected by ultrasonic C-Scan. In addition, analysis of variance (ANOVA) was applied to reveal the influential parameters and their effect levels. After conducting experiments using the Taguchi L18 test set, it was observed that the C2-coded specimen yielded better results in terms of maximum peak load, maximum displacement, and damage area. While the decrease in temperature increased the damage and maximum peak load, the increase in temperature did not cause a significant change in the maximum peak load. The primary damage mechanisms observed in damage investigations were matrix cracks and delamination between composite layers. Although delamination is present between the Al/CFRP layer, it is not significant. According to ANOVA results, impact energy was the most effective parameter for maximum impact force, maximum displacement, and damage area, with contribution rates of 81%, 74%, and 76%, respectively. The optimal experimental conditions (23°C temperature and 23 J impact energy with the C1-coded sample) were determined using grey relational analysis based on principal component analysis.

The aim of this study is to examine the low velocity impact behavior of aluminum honeycomb sandwich structures with glass fiber reinforced plastic (GFRP) face sheets with the help of finite element method. In the study, low velocity impact tests were carried out in the LS DYNA finite element program to examine the effects of face sheets thickness, core number, wall thickness, impact location and impact velocity on maximum contact force, absorbed energy efficiency and damage mode. Progressive damage analysis based on the Hashin damage criterion and the combination of Cohesive Zone Model (CZM) and the bilinear traction-separation law was performed using the MAT-54 material model. At the end of the study, it was determined that the face sheets thickness in sandwich structures had a significant effect on the impact resistance up to a certain impact energy. It has been observed that as the impact velocity gradually increases, there is a decrease in the contact force after a certain threshold value. As the impactor velocity increases, the energy absorption efficiency also increases. It has been determined that the location of the impact is very effective on peak force and energy absorption efficiency. The effect of the number of core layers depends on the face sheets thickness. When the face sheets thickness was not damaged at first contact, the peak force value increased in parallel with the number of layers. It was determined that the dominant damage mode after impact was matrix damage. It has been observed that as the energy level of the impactor increases, damage also occurs on the back surfaces.

In laminated composites used for aerospace structures, delaminations often occur by the impact under low and high velocities. Especially for the application of laminated composites to components of aeronautical turbo engines, the impact damage resistance is the primary design issue. Morita et al. [1] reported the damage resistance of CF/PEEK and CF/Toughened Epoxy laminates under low and high velocity impact tests. The report clarified that the relation between damage area (DA) and impact energy (IE) was linear, and the ratio DA/IE indicated the impact resistance for each specimen. Moreover, they reported that a ranking of impact resistance could be obtained both relatively and quantitatively among material systems tested in the work, and the ranking was dependent on impact velocity level. Masters [2] investigated the correlation of Compression After impact (CAI) strength and Mode II interlaminar fracture toughness in CFRP laminates. The work indicated that CAI strength could be estimated from Mode II interlaminar fracture toughness. However, the CAI strength is not usually used in designing of aeronautical turbo engines. It is desirable for the screening and selection of laminated composites in the designing to use a simple material property. 460In this reason, investigated in this study was the correlation of the damage resistance under low velocity impact and Mode II interlaminar fracture toughness in CFRP laminates. Three material systems, T800/3631 (CF/Epoxy), UT500/PEEK (CF/PEEK) and AS4/PEEK (CF/PEEK), were evaluated. This work consisted of three steps. The first step was to measure the damage resistance under low velocity impact of these material systems. The second step was to measure Mode II interlaminar fracture toughness of the laminates by conducting the End Notched Flexure (ENF) test. And the final step was to correlate the results obtained from low velocity impact tests and ENF tests.

The application of composite materials has increased so drastically in the aerospace industry. The Impact strength signifies the importance of composite materials when exposed to suddenly applied loads. This paper is focused on describing the behavior of interwoven kevlar/glass-epoxy and kevlar/basalt-epoxy composite laminate under high-velocity bullet impact. The composite lamina of kevlar/glass and that of kevlar/basalt are prepared using three different weaving techniques. The composite laminates are prepared using the compression moulding technique. The laminates have been subjected to high-velocity bullet impact. The velocity range is from 220 m/s to 260 m/s. The impact damage area in the laminate has been assessed through ultrasonic pulse echo submerged nondestructive technique. The impact strength has been calculated using the damaged area derived using the impact energy absorbed by the laminate. The results have shown that the maximum impact which found out to be kevlar/basalt (KB 1 × 1) is 28.24 J/cm2.

Low-velocity impact test on sandwich panels composed of aluminum face sheets and thermoplastic honeycomb cores have been performed to characterize the impact performance as a function of core thickness and drop heights. Impact parameters like maximum impact force, impact energy and impact damage area were evaluated and compared. Consequent damages were inspected visually on the impact surface as well as the rear surface. The experimental results found that panels with thicker core exhibited higher impact force than thinner core counterparts, allowing the panel to absorbed more energy. Higher degree of impact damage can be observed at elevated drop heights as most of the damage took the form of local core crushing, face sheet buckling and debonding between the face sheet and core,. Resulting damage area were different according to the core thickness as thicker core prone to absorbed more energy that lead to more damage propagation.

Banana fiber has a high potential for use in fiber composite structures due to its promise as a polymer reinforcement. However, it has poor bonding characteristics with the matrixes due to hydrophobic–hydrophilic incompatibility, inconsistency in blending weight ratio, and fiber length instability. In this study, the optimal conditions for a banana/epoxy composite as determined previously were used to fabricate a sandwich structure where carbon/Kevlar twill plies acted as the skins. The structure was evaluated based on two experimental tests: low-velocity impact and compression after impact (CAI) tests. Here, the synthetic fiber including Kevlar, carbon, and glass sandwich structures were also tested for comparison purposes. In general, the results showed a low peak load and larger damage area in the optimal banana/epoxy structures. The impact damage area, as characterized by the dye penetration, increased with increasing impact energy. The optimal banana composite and synthetic fiber systems were proven to offer a similar residual strength and normalized strength when higher impact energies were applied. Delamination and fracture behavior were dominant in the optimal banana structures subjected to CAI testing. Finally, optimization of the compounding parameters of the optimal banana fibers improved the impact and CAI properties of the structure, making them comparable to those of synthetic sandwich composites.

This study investigates the dynamic response of novel 3D natural fibre-reinforced hybrid composites. Two reinforcement techniques were employed: 2D intralaminar and 3D orthogonal-through-the-thickness (3D-OTT). Jute bidirectional fabric served as the primary fibre phase, while sisal and curauá fibres provided secondary reinforcement. The 3D-OTT architecture incorporated transverse fibres woven through-the-thickness of the fibre preforms, providing additional reinforcement. Pure jute composites (JFRP) were also tested for comparison. Low-velocity impact (LVI) tests, including perforation and repeated impact, assessed energy absorption, load-bearing capacity, and impact fatigue life. Results showed that 3D reinforcement effectively suppressed crack propagation during impact. 2D sisal fibre based architecture specimens demonstrated the highest absorbed energy and peak load during perforation due to fibre delamination, which created large energy-absorbing debonding areas. While CURAUÁ composites exhibited similar energy absorption and peak loads for both architectures due to strong fibre–matrix interlocking, SISAL composites showed lower energy absorption in the 3D configuration. Compared to a jute-based reference (JFRP), both CURAUÁ and SISAL composites demonstrated superior perforation resistance (30% and 50% increases, respectively). The 3D architecture significantly improved impact fatigue life, increasing it by 3.6× for sisal fibre and 2× for curauá based specimens. Micro-CT analysis revealed distinct crack- arrest mechanisms: 3D reinforcement reduced crack propagation in sisal fibre reinforced specimens, while curauá specimens benefitted from its strong fibre/matrix interface for natural crack arrest.