How high the frequency of the high-frequency fatigue testing machine can be?What is the difference between 100Hz/300Hz/1000Hz

"What is the frequency of a high-frequency fatigue testing machine?" "What is the difference between 100Hz and 300Hz equipment?" "Is there a 1000Hz ultra-high-frequency fatigue testing machine?" This is the most frequently asked question when purchasing a high-frequency fatigue testing machine.Frequency is one of the core parameters of high-frequency fatigue testing machines, which directly determines testing efficiency, equipment cost and scope of application.This article will systematically review the frequency levels, technical principles, applicable scenarios of different frequency bands, and key issues that need to be paid attention to when selecting high-frequency fatigue testing machines.

1. Frequency classification of fatigue testing machines

According to the operating frequency range, fatigue testing machines are usually divided into the following four levels:

2. Technical principles of different frequency bands

2.1 100Hz-300Hz: electromagnetic resonance mainstream frequency band

Currently, the most common high-frequency fatigue testing machines on the market operate at frequencies between 100Hz and 300Hz, and almost all of them use the principle of electromagnetic resonance (electromagnetic resonance).Its working principle is: the alternating electromagnetic force is generated by the electromagnet, which excites the mechanical system composed of the resonance spring, the mass block and the sample to produce resonance, and applies cyclic load to the sample in the resonance state.Due to the use of the resonance amplification effect of the mechanical system, the energy consumption of the electromagnetic resonance fatigue testing machine at high frequency is extremely low, only 1/5 to 1/10 of the electro-hydraulic servo type.

The 100Hz-300Hz frequency band is the golden frequency band for high-cycle fatigue testing.Taking 200Hz as an example, it only takes about 14 hours to complete 10⁷ cycles, while it takes about 11.5 days to use 10Hz electro-hydraulic servo equipment. The efficiency gap is huge.Therefore, for scenarios such as S-N curve testing of large quantities of metal materials and production quality inspection, a 100Hz-300Hz electromagnetic resonance fatigue testing machine is the first choice.

2.2 300Hz-1000Hz: advanced frequency band of electromagnetic resonance

The working frequency of some high-end electromagnetic resonance fatigue testing machines can reach 400Hz-1000Hz.To achieve higher frequencies, it is necessary to optimize the natural frequency of the mechanical system, use lighter masses, higher-stiffness resonant springs, and more sophisticated electromagnetic excitation systems.The higher the frequency, the higher the requirements for the machining accuracy, dynamic balancing performance and response speed of the control system of the mechanical system.

High-frequency fatigue testing machines above 300Hz are mainly used in scenarios that require extremely high testing efficiency, such as ultra-high cycle fatigue pre-screening of aerospace materials and rapid acceptance of large batches of fasteners.However, it should be noted that after the frequency exceeds 300Hz, the heating problem of the sample will become significant, which may affect the accuracy of the test data, and an air-cooling or water-cooling device is usually required.

2.3 Above 1000Hz: ultrasonic/piezoelectric ultra-high frequency

When the frequency requirement exceeds 1000Hz or even reaches 20kHz, the traditional electromagnetic resonance method can no longer meet the requirements, and ultrasonic/piezoelectric driving principles need to be used.The ultrasonic fatigue testing machine uses a piezoelectric ceramic transducer to convert electrical signals into mechanical vibrations, amplifies the amplitude through a horn, and applies ultra-high-frequency cyclic loads to the specimen in a resonance state.This type of equipment usually operates at 15kHz-20kHz and is mainly used for very high cycle fatigue (VHCF) research, which is a test of 10⁸ to 10¹⁰ cycles.

Ultrasonic fatigue testing machines are mainly used in scientific research institutes and high-end material research and development. They are expensive and have special requirements for the shape of the sample (usually need to be designed into a trumpet-shaped or dumbbell-shaped resonance sample), and are not suitable for routine industrial quality inspection.

3. Key considerations for frequency selection

3.1 Higher frequency is not better

Many buyers mistakenly believe that the higher the frequency, the better the equipment. In fact, the frequency selection must match the test requirements.According to GB/T 3075 Axial Force Control Method for Fatigue Testing of Metal Materials and ISO 1099 standards, the recommended frequency range for high-cycle fatigue testing is usually 30Hz-100Hz, and some standards allow up to 200Hz.Too high a frequency may result in:

• Sample heats up: The internal friction and heat of the material under high-frequency cycles may change the material properties and affect the accuracy of the data.

• strain rate effect: Different materials have different fatigue behaviors under different strain rates, and excessively high frequencies may not represent actual service conditions.

• Device restrictions: High-frequency equipment can usually only produce sine waves and cannot meet the loading requirements of complex waveforms.

3.2 Focus on "effective frequency" rather than "nominal frequency"

When selecting, pay attention to distinguishing between the nominal maximum frequency and the actual effective operating frequency of the device.The highest frequency of the electromagnetic resonance fatigue testing machine is the resonance frequency under a specific sample stiffness. During actual testing, the stiffness of different samples is different, and the resonance frequency of the system will also change.The specimen with high stiffness has a high resonance frequency, and the specimen with small stiffness has a low resonance frequency.Therefore, equipment with a nominal 300Hz frequency may only work at around 100Hz when testing some low-stiffness specimens.When purchasing, the actual operating frequency range under the target sample conditions should be confirmed with the manufacturer.

3.3 Trade-off between frequency and load

There is a trade-off between frequency and load.Generally speaking, the higher the frequency, the smaller the maximum test force.The electromagnetic resonance fatigue testing machine can easily achieve frequencies above 200Hz below 100kN, but when the load reaches 200kN-300kN, the frequency usually drops to around 100Hz.If large loads (above 300kN) and high frequencies (above 100Hz) are required to be met at the same time, the equipment cost will increase significantly, and the technology will be difficult, and customization is usually required.

4. About Shandong Huayan Intelligent Equipment Group

Shandong Huayan Intelligent Equipment Group Co., Ltd. is a professional testing machine R&D and manufacturing enterprise. The company's core team has 20 years of industry experience. Its products cover a full range of fatigue testing equipment such as electromagnetic resonance high-frequency fatigue testing machines and electro-hydraulic servo dynamic fatigue testing machines.Huayan's high-frequency fatigue testing machine adopts the principle of electromagnetic resonance, with an operating frequency covering 50Hz-300Hz and a load range of 10kN-300kN. It can meet various needs such as high-cycle fatigue testing of metal materials, S-N curve determination, and fatigue life verification of components.

Huayan Intelligent Equipment is located in Jinan and has complete R&D, production and measurement and testing capabilities. The group has Tianhua Measurement and Testing (Shandong) Co., Ltd., which can provide customers with one-stop services of equipment calibration, operation training and after-sales maintenance.The company has participated in the formulation of more than ten industry group standards, holds 17 national patents, and is the vice-chairman unit of the Shandong Electrotechnical Society.If you need to purchase a high-frequency fatigue testing machine, please contact us. Our engineers will recommend the most suitable frequency and load configuration for you based on your test materials, specimen size and cycle number requirements.

5. FAQ

Q1: High frequency fatigueTesting machineThe higher the frequency, the faster the test speed?

A: Under the same number of cycles, the higher the frequency, the shorter the test time.For example, to complete 10⁷ cycles, 100Hz takes about 27.8 hours, 200Hz takes about 13.9 hours, and 300Hz takes about 9.3 hours.However, frequency selection is limited by factors such as test standards, sample heating, equipment load, etc. High frequencies cannot be pursued blindly.

Q2: ElectromagneticResonancefatigueTesting machineWhy can't the frequency be adjusted at will?

A: The electromagnetic resonance fatigue testing machine works based on the resonance principle of the mechanical system. The resonance frequency of the system is jointly determined by the resonance spring stiffness, mass block mass and sample stiffness.After the specimen is replaced, the system stiffness changes and the resonance frequency will change accordingly.The equipment adjusts the frequency within a certain range by fine-tuning the mass block or spring preload, but the adjustment range is limited, usually around ±20%.

Q3: What should I do if the sample heats up during high-frequency fatigue testing?

A: Sample heating is a common problem under high-frequency cycling, especially when the frequency exceeds 150Hz.Solutions include: (1) Reduce the test frequency; (2) Equip an air-cooling device to cool the sample; (3) Use intermittent loading to allow the sample time to dissipate; (4) Use thermocouples to monitor the sample temperature in real time to ensure that the temperature is within the allowable range of the standard.Huayan Intelligent Equipment's high-frequency fatigue testing machine can be equipped with an air cooling system and a temperature monitoring module.

Q4: Electro-hydraulic servo fatigue at 100HzTesting machineand 100Hz electromagneticResonanceWhat is the difference between fatigue testing machines?

A: Although the frequency nominals are the same, the working principles and performance of the two are very different.The electro-hydraulic servo type is close to its upper frequency limit at 100Hz, and long-term high-frequency operation will accelerate the wear of the servo valve and seals, resulting in high energy consumption; the electromagnetic resonance type is in a comfortable working range at 100Hz, with low energy consumption and simple maintenance.In addition, the electro-hydraulic servo type can handle complex waveforms and large loads, while the electromagnetic resonance type mainly handles sine waves with medium and small loads.If only standard high-cycle fatigue sinusoidal testing is performed, the electromagnetic resonance method is more efficient and cheaper.

Q5: Ultrasound fatigueTesting machineCan (20kHz) replace ordinary high-frequency fatigue testing machines?

A: It cannot be completely replaced.The ultrasonic fatigue testing machine has an extremely high frequency (15kHz-20kHz) and is mainly used for ultra-high cycle fatigue (VHCF) research of more than 10⁸ times. However, it has special requirements for the shape of the specimen (requiring resonance specimen design). The test method is different from conventional axial fatigue, and the data cannot be directly compared with standard high-frequency fatigue testing.For routine high-cycle fatigue testing (10⁶-10⁸ times), it is still recommended to use an electromagnetic resonance fatigue testing machine of 100Hz-300Hz.