Ultrasonic Fatigue Test for Hourglass-shaped Metal Test Specimens with Parallel Sections

User Benefits

- The ultrasonic fatigue tester is capable of testing at a repetition rate of 20 kHz and can complete tests with 10⁹ cycles (1 billion cycles) in only about 14 hours. - It is possible to test hourglass-shaped test specimens with parallel sections specified in the Chinese National Standard GB/T 43896 “Metallic materials-Very high cycle fatigue-Ultrasonic fatigue test method.”

Introduction

Fatigue is a fracture phenomenon caused by repeated loads, even within the elastic region. It is said that about 70 % of structural fracture phenomena are caused by metal fatigue. For most structural steels, there is a fatigue limit where fatigue failure does not occur even after repeated loading if the stress is less than a certain value, and the number of cycles is about 10⁶ to 10⁷. However, in high-strength steels such as chromium molybdenum steel, it is known that fatigue failure occurs in the ultra-high cycle range of 10⁸ to 10⁹ cycles, exceeding 10⁷ cycles, due to inclusions in the material. Therefore, the standard of 10⁷ repetitions as the maximum number of repetitions used in general fatigue tests is not sufficient, and fatigue tests with more than 10⁹ cycles are required. On the other hand, a fatigue test with more than 10⁹ cycles would take more than 3 years at a 10 Hz load. The ultrasonic fatigue tester used in this study is capable of testing at 20 kHz and can complete tests with 10⁹ cycles in about 14 hours, making it ideal for measuring ultra-high cycle fatigue. In previous reports, we conducted tests on standard hourglass specimens. In November 2024, the National Standard GB/T 43896 of the People's Republic of China (Metallic materials- Very high cycle fatigue-Ultrasonic fatigue test method) was issued, so Shimadzu has added a new dimension calculation function for hourglass-shaped specimens with parallel sections to its USF-2000A dedicated software, Super Sonic. In this paper, we introduce an example of measurement of an hourglass-shaped specimen with a parallel section in compliance with GB/T 43896 using SNCM439, a type of structural steel.

August 26, 2025 GMT