No abstract

No abstract

This work presents a novel conical rotor non-contact piezoelectric actuator based on the principle of near-field acoustic levitation. The conical rotor is levitated and driven by a single stator, while generating two orthogonal standing waves and superimposing a travelling wave vibration on the stator. A frequency sensitivity analysis is conducted for the stator structural parameters, based on a dynamics calculation. An acoustic field simulation is conducted and the sound pressure distribution is obtained. The acoustic radiation force is calculated at different voltages and frequencies. A prototype is fabricated, and the vibration characteristics are experimentally obtained. A test system is built for the actuator, and the conical rotor successfully achieves levitation and rotation. The levitation height and rotation speed of the 3.37[Formula: see text]g rotor are 0.4[Formula: see text]mm and 2300[Formula: see text]r/min, respectively. The acoustic simulations are validated experimentally and show reasonable agreement.

No abstract

The ballistic performance of protective structures under multiple projectile impacts attracts increasing attention due to its practical importance, and existing studies were seldomly devoted to exploring how the structure would deform and fail when subjected to such loads. This study aimed to characterize the multi-hit ballistic resistance of fully-clamped thin plates made of 304 stainless steel using finite element method, with the equivalent plastic strain employed to define material damage and failure/fracture. The numerical model was validated against existing experimental results of double impacts at the same location, with good agreement achieved. The model was subsequently employed to quantify the effects of impact position, interval time between successive hits, projectile nose shape (e.g., spherical, flat and conical), and boundary condition of target plate on ballistic limit and deformation/failure modes. Further, ballistic limit boundaries were constructed for both double and triple impacts of projectiles. Obtained results are helpful for designing high-performance protective structures against multiple projectile impacts.