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Composite sandwich structures have gained significant attention in engineering applications due to their exceptional strength-to-weight ratio, stiffness, and energy absorption capabilities. One promising core material is cork, which possesses desirable characteristics such as low density, high compressive strength, and good energy absorption capacity. This study aimed to compare the impact performance of composite shells with composite sandwich shells featuring an agglomerated cork core, while investigating the influence of semicylindrical shell diameters. The results underscore the significant impact of specimen diameter on the performance of these structures. Larger diameter specimens (106 mm) exhibited notably higher maximum force, albeit with lower maximum displacement, energy absorption, and contact time compared to those with smaller diameter (82 mm). Similar trends were observed in composite sandwich shells. Furthermore, the inclusion of cork in composite sandwich shells marginally reduced strength of the specimens. For identical diameters, both configurations exhibited comparable maximum force and displacement. However, composite sandwich shells with a cork core absorbed less energy than those without a cork core. This behaviour persisted across both shell geometries, with slightly higher percentage differences observed in the larger diameter specimens.

This study investigates the effect of damage interference resulting from impact loads on the mechanical response and impact fatigue life of E-glass/epoxy composite laminate shells. The analysis involves single impacts at different points to evaluate the impact strength's dependency on boundary conditions. Notably, there is a gradual reduction in both maximum impact force and absorbed energy beyond 10 mm from the centre, towards unconstrained edges, accompanied by an increase in displacement. Specifically, at a distance of 30 mm, the maximum force and absorbed energy register a decrease of 9.4% and 7.9%, respectively, while the displacement rises by 14.5%. The findings reveal that the damage severity decreases as the impact point is closer to the unconstrained edge of the specimen, which can be attributed to a stiffness reduction, which can reach up to 22%. Symmetrically induced pre-damages exhibit no discernible effect on the subsequent impact response. It is observed that beyond 10 mm from the shell's centre, the number of impacts required to reach puncture increases by 10.5% and 21.1% for distances of 20 and 30 mm, respectively. Furthermore, it is also found that alternating impacts between symmetrical points show no inclination towards a preferential point for puncture.

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 0º, particularly in the upper half of the laminate. The laminates with a 45º orientation in the upper layers present the lowest displacement values, whereas the laminates with the upper layers oriented at 0º 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 45º exhibit slightly higher energy dissipation due to intralaminar damage (fibre failure) and interlaminar damage (delamination).

Nowadays, composite materials are increasingly used in the most diverse areas of engineering, where non-planar geometries begin to be quite frequent. However, the existing knowledge about its mechanical performance is still not enough for structural applications. Therefore, experimental tests were carried out to study the thickness effect on static compression and multi-impact response of laminated E-glass/Polyester semicylindrical shells. For this purpose, specimen with thicknesses of 1.1 mm, 1.6 mm and 2.1 mm (corresponding to 6, 9 and 12 woven fabric layers) were considered. In terms of static response, higher thicknesses are responsible for higher compressive strength and stiffness, reaching, in the first case, differences of 252.6 % between the thinnest and thickest shells. Regarding the multi-impact response, the impact fatigue life increases 17.4 times for the analysed thickness range, which can be explained by the different damage mechanisms observed. It was observed that impact damage becomes more localized with increasing thickness, because the energy is dissipated by more interfaces.

Literature is not abundant on the mechanical characterization of cylindrical shells for civil engineering applications, especially in terms of impact response. In this context, this study intends to evaluate the impact response of cylindrical sandwich shells produced with various types of fibers. Analysis was done on three alternative configurations: carbon fibers only, carbon fibers and glass, and carbon fibers and basalt. All configurations were tested for static and impact strength. It was concluded that the constituents of the cylindrical sandwich shells are determinants in both static and impact strength. In terms of compressive properties, the lowest displacement (4.4 mm) and highest compressive strength (873 N) and stiffness (354 N/mm) are attributed to configuration 6C. However, the incorporation of basalt fibers decreased these properties to the lowest values, and reductions of 22% and 44% were found for the compressive strength and stiffness, respectively, while the displacement increased around 66%. On the other hand, in terms of impact, significant benefits were achieved with the introduction of glass fibers. Compared to configurations 6C and 2C+2B+2C, for instance, the elastic recuperation was 25% and 64.6% higher, respectively.

This paper presents an efficient and reliable approach to study the low-velocity impact response of woven composite shells using 3D finite element models that account for the physical intralaminar and interlaminar progressive damage. The authors’ previous work on the experimental assessment of the effect of thickness on the impact response of semicylindrical composite laminated shells served as the basis for this paper. Therefore, the finite element models were put to the test in comparison to the experimental findings. A good agreement was obtained between the numerical predictions and experimental data for the load and energy histories as well as for the maximum impact load, maximum displacement, and contact time. The use of the mass-scaling technique was successfully implemented, reducing considerably the computing cost of the solutions. The maximum load, maximum displacement, and contact time are negligibly affected by the choice of finite element mesh discretization. However, it has an impact on the initiation and progression of interlaminar damage. Therefore, to accurately compute delamination, its correct definition is of upmost importance. The validation of these finite element models opens the possibility for further numerical studies on of woven composite shells and enables shortening the time and expenses associated with the experimental testing.

This paper aims to analyse the low-velocity impact performance of 3D printed continuous carbon fibre reinforced composites manufactured by fused deposition modelling. Moreover, the effect of ageing on the impact properties and visual damage is studied. This evaluation is crucial for understanding the long-term behaviour and durability of these materials, enabling better design and engineering decisions in various applications where impact resistance is paramount. Low-velocity impact tests were conducted on specimens aged 1, 7, 15 and 30 days. An instrumented drop-weight testing machine was employed for the tests. The dimensions and layup sequence of the composite specimens were designed following the recommendations outlined in the ASTM D7136/D7136M standard for unidirectional composite tapes. Results showed that the initial elastic part slightly reduces with age. In addition, the severity of visual damage in the specimens clearly varied with age. The older specimens present the less visible damage but also the lower impact energy absorption. Keywords: 3D printing, Fused deposition modelling, Composites, Ageing, Low-velocity impact

The effect of the interface stiffness and interface strength on the low-velocity impact response of woven-fabric semicylindrical composite shells is studied using finite element (FE) models generated with continuum shell elements and cohesive surfaces. The intralaminar damage is accounted for using the constitutive model provided within the ABAQUS software, while the interlaminar is addressed utilising cohesive surfaces. The results show that the interface stiffness has a negligible effect on the force and energy histories for values between 101 N/mm3 and 2.43 × 106 N/mm3 . However, it has a significant impact on the delamination predictions. It is observed that only the normal interface strength affects the maximum impact force and the delamination predictions. Increasing its value from 15 MPa to 30 MPa resulted in an 8% growth in the maximum force, and a substantial reduction in the delaminated area. The obtained results serve as guidelines for the accurate and efficient computation of delamination. The successful validation of the FE models establishes a solid foundation for further numerical investigations and offers the potential to significantly reduce the time and expenses associated with experimental testing.

This paper investigates the impact dynamics of thin semicylindrical woven composite laminate shells, with a particular focus on understanding the influence of thickness. Utilizing the finite element (FE) method, the study evaluates both intralaminar and interlaminar damage associated with the impact response. The findings show that the implementation of the explicit FE method, along with a continuum damage mechanics model, for the intralaminar damage, and a surface-based cohesive model, for the interlaminar damage, may be used to correctly predict the load histories, as well as the maximum impact force, maximum displacement, contact time and impact bending stiffness (IBS). The numerical predictions reproduce well the linear response of the maximum impact force and maximum displacement to the thickness variation, as well as the 2nd order polynomial curve of the IBS, with errors ranging from 2.7% to 15.9%. Moreover, the damage areas and the effect of thickness on the damage severity were accurately replicated. These results’ validation enables the prediction of the energy histories and the ensuing energy dissipation forms. According to the findings, the intralaminar damage is around 5 times more significant than the other energy dissipation forms. The accuracy of the simulation creates the possibility for more impact investigations using a similar numerical approach, reducing the expenditures of experimental testing.

This study delves into the effect of repeated low-velocity impacts on the residual tensile strength of composite laminates reinforced with E-glass/epoxy woven fabrics. The specimens underwent a series of low-velocity impacts, each delivering a constant energy of 4 J. Various parameters, such as maximum impact load, displacement, contact time, and absorbed energy, were examined. The residual tensile strength was subsequently analysed for each impact and compared to control specimens that experienced no impact. The results highlighted a significant decrease in residual tensile strength after the initial impact, whereas subsequent impacts exhibited a diminished effect until the puncture of the specimens occurred.

The effect of multiple low-velocity impacts on the tensile strength of E-glass/epoxy woven fabric composite laminates was studied. For this purpose, specimens with a lay-up sequence of [0,90]10 were considered, which were subjected to multiple impacts with an energy of 4 J. For a better understanding of the phenomenon, the impact tests were analysed in terms of maximum load and displacement, contact time and energy absorbed. Finally, the residual tensile strength of the specimens was evaluated after each series of impacts, and the results were compared with those obtained in the control specimens (without impacts). It was possible to conclude that the residual tensile strength is strongly affected after the 1st impact, while the damage introduced in the following impacts is not so expressive and, consequently, affects the residual strength less.