Tham khảo tài liệu 'volume 08 - mechanical testing and evaluation part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Ultrasonic Fatigue Testing Historical Perspective Development of higher-frequency testing machines began early in the 20th century. Prior to 1911 the highest fatigue testing frequency was on the order of 33 Hz using mechanically driven systems. Electrodynamic resonance systems appeared in 1911 when Hopkinson Ref 1 introduced a machine capable of 116 Hz. In 1925 Jenkin Ref 2 tested wires of copper iron and steel at 2 kHz using similar techniques. In 1929 Jenkin and Lehmann Ref 3 were able to test materials up to 10 kHz using a pulsating air resonance system. Mason Ref 4 achieved ultrasonic frequency 20 kHz in 1950 with the adaptation of magnetostrictive and piezoelectric-type transducers to fatigue testing. This method translated 20 kHz electrical voltage signals into 20 kHz mechanical displacements. A displacement-amplifying acoustical horn and the test specimen were driven into resonance by the transducer. This concept has remained basically unchanged and is the foundation of the practices used in modern ultrasonic fatigue test technology. In the early 1960s frequencies as high as 92 and 199 kHz were employed for fatigue tests using Mason s techniques Ref 5 6 These extremely high frequencies surpass the upper limits of practicality because of the constraints of specimen size frequency is inversely proportional to specimen length machining tolerances strain amplitude measurements and energy considerations. A review of the ultrasonic fatigue testing in the 1970s and 1980s shows that the majority of test stands operate at frequencies between 17 and 25 kHz. This unofficial standard is primarily dictated by the availability of commercial high-power ultrasonic transducers and power supplies. These frequencies are also desirable from a safety viewpoint because they are above the range of normal human hearing. Fatigue testing at 20 kHz proceeds quietly in comparison to testing at 1 to 10 kHz. References cited in this section 1. B. Hopkinson Proc. R. Soc. London A Vol 86 .
