# Design and Experimental Study of a Down-Drive Piezoelectric High-Frequency Fatigue Testing Machine
## 1 Introduction  
In recent years, with the development of microelectromechanical technology and biomimetic technology, products such as microatuators [1, 2], microsensors [3], and bionic fish [4] have emerged. The development of technologies for testing the mechanical properties of these products under near-service conditions has become extremely urgent. Fatigue testing is an important method to study the mechanical properties of materials [5, 6]. Due to the complexity of the fracture conditions of materials [7], fatigue testers have been designed to test them in bending [8, 9], torsion [10], or tension [11, 12]. Tensile fatigue studies of products are very helpful in recognizing the safety of steel sheet assemblies, and uniaxial test methods are still widely used compared to the complexity of biaxial bending tests. In the case where uniaxial pure tensile loading is considered, the specimen is clamped in the fixture of a fatigue testing machine, and cyclic tensile stresses at a fixed frequency generated by the fatigue testing system are applied to the specimen in order to fail the specimen and calculate the fatigue life. The variable load applied to the specimen by the fatigue tester is essentially generating a vibrator load. In the current research, uniaxial fatigue tester drives are mainly categorized into three types, \"electromagnetic drive\" [13, 14], \"electro-hydraulic servo drive\" [15, 16], and \"piezoelectric drive\" [17]. Among them, the electromagnetically driven type is characterized by fast response and is suitable for routine material testing, and it is also the most commonly used fatigue test equipment; The electro-hydraulic servo-driven type has a larger output power and is suitable for the inspection of large, medium, andheavy loaded parts, but with a low operating frequency and a long testing time, the range of applications is more restricted. Piezoelectric materials are often used as high-speed and -precision actuators due to their fast response, lack of electromagnetic interference, high resolution, and high deformation accuracy [18]. As a result, researchers favour fatigue testing machines that use piezoelectric materials as the drive source. Piezoelectric fatigue testers can be categorized into three types: the first one is piezoelectric ceramic ultrasonic transducer-driven fatigue testers [19; 20], the second is piezoelectric stack-driven fatigue testers [21], and the third one is piezoelectric vibrator-driven fatigue testers [22]. [PERSON] [17] designed a circular piezoelectric vibrator-driven fatigue testing machine, adjusting the frequency of the alternating voltage acting on the piezoelectric vibrator to induce the resonance of the whole system, and the inertial force generated by the mass of the elastic loader in the resonance state is reciprocated on the specimen, thus realizing fatigue testing. [PERSON] [23] designed a piezoelectric-driven horizontal fatigue tester, which avoids the interference of the mass of the fixture in the vertical structure for static or dynamic loading. [PERSON] [24] proposed a new type of piezoelectric high-frequency micro load fatigue testing machine; the specimen is only subjected to alternating stress in the horizontal direction, avoiding the influence of other factors on the loading of the specimen, to ensure that the specimen fatigue test results are accurate. Most of the existing fatigue testing machines at home and abroad are designed for macro-scale devices, the dynamic loading is generally more than 500 N; the development of a more mature piezoelectric fatigue testing machine with a dynamic load greater than 100 N, and the development of piezoelectric fatigue testers for the range of less than 100 N, are still in the exploration stage.