## 1 Introduction  
Composite materials are widely used in aerospace structures due to their high strength-to-weight ratio [1; 2]. However, their impact damage tolerance has been a major concern in engineering applications. It is well-known that the mechanical properties of composite laminates deteriorate and the structural stability of composite laminates decreases for the case of the low-velocity impact loading. In applications, the loading conditions are multitude and complex, such as impacts by dropped tools during maintenance, collision from gravels on the runway during takeoff and landing, bird strike, and impact of hails during flight [3; 4]. Thus, improving the impact resistance and energy absorption capability of composite laminates is a very important task. In the early 1960s, [PERSON] et al. [5; 6] discovered the shape memory effect in an equiatomic Ni-Ti alloy. Afterward, it was discovered in some research studies that the Ni-Ti alloy exhibited fully recoverable transformation strains up to 8%, which could be also obtained in various forms, such as wires, strips, rods, tubes, and plates [7]. Due to the unique properties of shape memory alloy (SMA) wires, it was speculated that it may enhance the impact resistance of composites. Some studies on the impact response of SMA-reinforced composites have been reported in the literature. It is found that the impact resistance and energy absorption capability of composite laminates can be improved by embedding SMA into the composites. In the past three decades, a few experimental investigations were carried out for the impact response of SMA-reinforced composites. [PERSON] et al. [8] investigated the effect of super-elastic SMAs on the impact behavior of fiber-reinforced composites. The results suggest that SMAs have a positive effect on the maximum absorbed energy. [PERSON] et al. [9] identified the effect of SMAs on the damage behavior of laminates subjected to low-velocity impact at low temperatures of 293 K, 263 K, and 233 K. It is found that the impact damage behavior of the base laminates was slightly affected by the temperatures, but the deformation and damage of SMA laminates was affected by the temperatures. [PERSON] et al. [10] evaluated the influence of the integration of thin super-elastic SMA wires into laminated composites on the impact behavior of the hybrid composites, and distinguished the influence of the martensitic transformation from the introduction of a pure metallic wire and super-elastic SMA wire by embedding unidirectional steel wires into the polymeric matrix. They also investigated the influence of the integration of thin super-elastic wires on preventing damage propagation in composite structures [11]. It was found that the super-elastic SMA fibers can absorb much more strain energy than other fibers before their failure. [PERSON] et al. [12] found that the deflections of composite structures can be significantly reduced by changing the SMA volume fractions and temperature. [PERSON] et al. [13] showed that the damage resistance of the SMA-reinforced composites under low-velocity impact can improve for some cases. [PERSON] et al. [14] found that the impact resistance of the hybrid composites can improve by embedding the SMA fibers into composites. Moreover, a few numerical investigations on the low-velocity impact responses of SMA-reinforced composites have been also conducted. For example, [PERSON] et al. [15] conducted the finite element simulation for SMA-reinforced composite plates under low velocity impact. It is found that the impact damage of composites can be reduced significantly by embedding super-elastic shape memory alloys into a composite structure. [PERSON] et al. [16] studied the low-velocity impact behavior of a shape memory alloy hybrid composite by using the Abaqus/Explicit program. [PERSON] et al. [17] studied the accurate eccentric impact behavior for the preloaded SMA composite plates based on a novel mixed-order hyperbolic global-local theory. [PERSON] et al.