Ultrasonic fatigue testing machine is used to carry out the fatigue characteristics, fatigue life, prefabricated crack and crack extension test of metal and alloy materials and their components under tensile, compression, or tensile-compression alternating load at room temperature.
The traditional fatigue test technology can no longer meet the current requirements for modern machinery and equipment parts, ultra-long life, and ultra-high reliability requirements. Ultrasonic fatigue test is a kind of accelerated resonance type fatigue test method, which can significantly reduce the test time and is the only available solution for aero-engine blade ultra-long life fatigue test.
Table of Contents
- 1 The significance of conducting metal fatigue tests
- 2 Ultrasonic fatigue test principle
- 3 Advantages of ultrasonic fatigue testing
- 4 Main applications of the ultrasonic fatigue test method
The significance of conducting metal fatigue tests
Metal Fatigue Causes Air Crashes
Pictured is flight 1380 (Boeing 737-700) from New York-LaGuardia Airport to Dallas Love Field Airport on April 17, 2018.
The picture shows the loss of fan blade #13 from engine #1. There was evidence of metal fatigue in the area where the blade ruptured. The fan blades of the accident engine have accumulated over 32,000 engine cycles since the new installation.
The importance of metal fatigue test
Aviation gas turbine engine is the central power unit of airplanes and helicopters. It is a crucial piece of equipment that has long restricted the development of my country's aviation industry and military equipment. An aero-engine is a high-speed rotating machine with multiple rotors and frequent changes in operating conditions. Its components (especially blades and disks) are subject to very complex vibration loads.
The material fatigue problem caused by vibration load is the critical problem that restricts the high reliability and long service life of aero engines. It has long plagued the development and production of China's aero engines and their safe use.
Blade fatigue factors
High circumferential fatigue (HCF) and ultra-high circumferential fatigue (VHCF) are mainly caused by vibration stresses induced by various aerodynamic and mechanical sources, which can reach frequencies of several kilohertz. It can lead to fatigue fracture of essential engine components (fan, compressor, turbine blades or disks, and ducts) and even flight accidents.
- Engine internal flow disturbances
- Self-excited vibrations (chattering and jitter flow separation)
- Flow distortion (pressure)
- Rotor imbalance
Ultrasonic fatigue test principle
Ultrasonic fatigue test is an accelerated resonance fatigue test method, which establishes a mechanical resonance wave on the loaded sample. Based on the principle of piezoelectric stretching and using high-energy ultrasonic resonance technology, its testing frequency (20kHz) far exceeds the frequency of conventional fatigue testing. The fatigue degree and data near the threshold can be obtained within the actual test time. Due to the high frequency, the fatigue limit of various industrial materials with high repetition cycles can be quickly detected.
Ultrasonic fatigue testing machine is based on the principle of ultrasonic resonance, which generates high-frequency vibration load on the sample to complete the (ultra) high cycle fatigue performance test of the material. Meet the requirements of modern mechanical equipment for ultra-long life and ultra-high reliability of parts.
Our company developed the third generation of multi-functional ultrasonic fatigue tester with a wide range of working frequency, output amplitude, high control accuracy, can carry out a variety of metal materials and composite materials of variable stress ratio axial symmetric tensile compression, irregular stress ratio three-point bending, vibration bending and other forms of loading ultrasonic fatigue test. Simultaneously, to provide axial tension, three-point bending, vibration bending, and different types of specimens of the additional optimization design software.
Advantages of ultrasonic fatigue testing
- Random variable amplitude loading, including low-level loading, can be made closer to the engineering reality.
- Fatigue damage caused by minor defects can be reproduced simply by using a computer to set and control the test.
- Since the test is conducted in a resonant state, high stresses can be generated, and the 1000 MPa class's steel tests can be performed.
- The test equipment requires low output power (tens to hundreds of watts), saving a lot of energy and test money.
- At the end of the specimen during resonance, the stress level is shallow, simplifying specimen clamping, requiring only one end to be clamped, which is advantageous for brittle materials.
- Rapid evaluation of metallic materials' fatigue life with a repetition frequency of 20 kHz reduces the test time hundreds or thousands of times.
Take the 109 fatigue test as an example
1.5 years for a 20 Hz servo-hydraulic fatigue test;
231 days required for 50Hz rotary bending test machine;
300Hz high-frequency shaking table takes 38.5 days;
20Khz ultrasonic fatigue test takes only 13.8 hours.;
Main applications of the ultrasonic fatigue test method
It is mainly used in aerospace, high-speed railway, automobile, and power station to carry out (ultra) high cycle fatigue performance tests on various metal materials such as alloy steel, aluminum alloy, and titanium alloy, as well as carbon fiber composite materials. Compared with the conventional fatigue test method, it can shorten the test time by more than 90% and save the test cost significantly.