Composites are widely used in the fields of aviation and spaceflight because of their excellent specific strength and modulus. However, they are very sensitive to low-velocity impact damage, causing a potential threat as barely visible impact damage (BVID) [1
], which is defined as impacts that show minimal surface damage but which can cause the internal structure to suffer a complex failure [4
]. In addition, BVID can reduce the residual strength of the structure significantly [5
]. Hybrid composites are made of two or more different types of fibers in a common matrix. The hybrid structure mainly includes the interlayer and intralayer hybrids, and the sandwich structure is a special form of the interlayer hybrids [6
]. Intralayer hybrids are obtained by co-weaving and blending with multiple fibers in each layer [8
]. The purpose of hybridization is to obtain a new material retaining the advantages of its constituents. Glass fiber has low fracture strength and modulus, but carbon fiber has high stiffness and strength [10
]. Thus, hybrids including carbon fibers are fabricated most frequently with glass fibers, which are typically reported to improve most mechanical properties [12
]. This is especially true for the next generation of commercial aircraft, wind-power blades, and some lightweight car parts.
Various studies on the low-velocity impact behavior of hybrid composites have been conducted, concerning the sample size, material, and impactor type, most of which having focused on the effect of the stacking sequence [14
], especially for the interlayer hybrid structure [15
]. Jiang et al. [16
] compared the energy absorption in the sinusoidal plate with different stacking sequences, where it was shown that different stacking sequences had significant influences on failure modes and energy absorption capability. Riccio et al. [17
] analyzed the mechanical behavior of laminates with different impact energy, and it was discovered that matrix damage to the single ply was obviously influenced by the given stacking sequence. In the work carried out by Fiore et al. [18
], the aging resistance of jute-basalt interply hybrid laminates was studied, and it was found that the sandwich structure of the basalt hybrid performed best in terms of their mechanical performance compared to other generic composites. González et al. [19
] evaluated the drop-weight impact response of interply hybrid laminates manufactured using polymer matrix composite materials. In a study by Özben [20
], the effect of the misalignment angle of adjacent layers was examined by using two different fibers at the impact surface. The results showed that the impact performance of the laminate with glass fiber in the outer layer was greatly affected by the layer angle, whereas the carbon fiber at the outer layer could decrease the deformation of the laminate by increasing the misalignment angle. Sarasini et al. [21
] compared the impact and bending response of basalt/carbon hybrid composites and found that the bending performance of the sandwich hybrid structure was good, whereas the damage tolerance of the interlayer hybrid structure was better. Swolfs et al. [22
] proposed that an improvement in impact performance could be achieved by increasing the fracture toughness, and the impact resistance of hybrid composites was superior to the predicted value via hybrid law.
Extensive studies have been carried out to investigate the impact damage of hybrid composites [23
]. Zhu et al. [25
] assessed the impact behavior of Ti/M40 hybrid composites and found that the poor interlaminar forces were the main reason for the damage failure. Sayer et al. [26
] used three materials including carbon fiber, glass fiber, and aramid fiber to design the hybrid composites and found that the delamination and fiber breakage on the bottom surface were the major damage mechanism. Sun et al. [27
] proposed five types of aramid/polyethylene hybrid structures and found that the impact damage area was closely related to the hybrid structure, and that the damage area of the interlayer hybrid structure with aramid fiber on the impact surface was relatively small. Yang et al. [28
] reported that the anti-delamination performance of carbon/glass interlayer hybrid laminates was correlated with the deformation properties of two fibers.
Most of the previous studies emphasized the interlayer hybrid structures. However, the low-velocity impact properties on intralayer hybrid composites have been rarely investigated due to the complex processing [29
]. The fibers in non-crimp fabrics (NCFs) without buckling are all linked by knitted yarns, and the impact resistance can be improved by using the appropriate hybrid structure [31
In this study, the low-velocity impact properties of carbon/glass fiber interlayer, sandwich and intralayer hybrid composite laminates were investigated. Load and energy versus time curves were recorded, and the important impact parameters like absorbed energy and peak load were studied in detail. In addition, the impact damage mechanisms of different hybrid structures were revealed by visual inspection, C-scan, and micro-CT techniques.
The behavior of interlayer/intralayer hybrid composites based on carbon and glass non-crimp fabric under low-velocity impact was studied.
The interlayer hybrid structure exhibited a better impact performance compared to the sandwich hybrid structure due to the more numerous of C-G hybrid interfaces. I-C showed the biggest peak load with small damage, whereas the S-C showed the highest energy absorption with more internal damage. A better impact resistance can be achieved by deploying a suitable C-G interface.
The intralayer hybrid structure had in-plane and interlayer C-G hybrid interfaces, resisting the propagation of the stress wave in both transverse and longitudinal directions. The peak load of the 1:1 was slightly less than that of the CF due to the small unit width of the fiber bundle. In contrast, the 2:2 structure decreased the resistance to the stress wave propagation and improved the energy absorption.
The delamination of the interlayer hybrid structure was affected by the stacking sequence. The S-C structure had the largest delamination area. In addition, the internal damage of the intralayer hybrid structure was affected by the impact location and the hybrid structure, the hybrid structure having a dominant effect.
The 1:1 structure had a higher peak load and the smaller damage area compared to I-C under the same hybrid ratio and impact energy level, indicating a higher impact resistance as compared to the other hybrid structures. In general, a better impact resistance can be achieved by designing an appropriate intralayer hybrid structure with a constant hybrid ratio. Meanwhile, because hybrid composites will be used over the long term, later studies should investigate the stability property.