## 1 Introduction  
The fan-containment casings of commercial aero-engines, which is a typical thin-walled structure [1], are typically made of two-dimensional (2D) triaxial braided composite materials [2]. To be certified as airworthy, the fan casing must demonstrate that it can resist the impact due to a blade-out event [3]. The application of braided composite materials in aviation thus requires an in-depth investigation of the failure mechanism of these materials under impact loading [4, 5]. Verification in the final stages of structural design usually requires full-scale tests and component-level rig tests, which are extremely expensive and require specialized testing equipment [6, 7]. Alternatively, ballistic-impact tests on subscale and full-scale components allow designers to optimize the design of composite structures. Numerous ballistic-impact results have demonstrated that target-panel failure is related to the characteristics of both target and projectile, as well as the impact conditions, including the impact velocity and attitude of the projectile. Previous studies [8] also suggest that, under impact loads,textile composites resist delamination better than laminated composites but exhibit more complicated failure modes. Given that impact behavior is vital to the assessment of aero-engine safety, ballistic-impact tests must be conducted on triaxial braided composites to identify their failure modes and energy-absorption characteristics. Although numerous efforts have focused on the mechanical properties and failure modes of triaxial braided composites [9; 10; 11; 12; 13; 14], a few studies have investigated their impact behavior [15; 16]. During impact events, a remarkable strain rate effect at high loading rate is reported in composite materials [17]. In ballistic impact tests, axisymmetric metal projectiles are the most common projectiles used. [PERSON] et al. [18] used metal projectiles in impact tests of 2D hybrid-glass-carbon-braided composites and found that the damage area increases roughly linearly in impact energy and, for a given impact energy, is greater for lighter impactors. [PERSON] et al. [19] conducted impact experiments on triaxially braided polymer-matrix composites to study the heat generated in material due to projectile velocity and penetration damage. Note that all the ballistic-impact studies cited above used axisymmetric impactors, such as cylinders or spheres, which facilitates control of the impact attitude. Gelatin projectiles are typical artificial-bird projectiles used for studying issues related to bird strikes [20; 21; 22; 23], thus were also used in evaluating. [PERSON] et al. [24] performed impact tests using cylindrical gelatin projectiles to identify the failure modes of composite plates and half-rings fabricated in a triaxial braided architecture and found that fiber tensile failure occurs in the back fly for both composite plates and half-rings, whereas damage is localized near the impact site as opposed to extending to the boundaries. Such tests using gelatin projectile are designed to induce a high rate of deformation, similar to that experienced by a jet engine fan case during a fan blade-out event. [PERSON] [25] used gelatin projectiles to examine the impact resistance of a 2D triaxially braided composite panel with different braiding angles and matrix resins, and the impact results were used to validate the proposed methodology, which was called \"simplified braiding through-thickness integration points\" [26]. [PERSON] et al. [27] also used gelatin projectiles to measure the impact and high-strain-rate properties of triaxial braided composites and quantified the degradation caused by thermal and hygroscopic aging during service. Besides gelatin projectiles, a more appropriate impactor for simulating a fractured engine rotor blade is a metallic plate projectile, such as a titanium alloy blade-like projectile [28; 29; 30; 31; 32] when investigating the impact resistance of candidate materials for an engine casing.