The residual stress generated in the workpiece by mechanical processes can reduce the strength of the workpiece, resulting in process defects such as deformation and cracking; On the other hand, the natural release process may cause changes in the size of the workpiece or reduce its mechanical properties such as fatigue strength and stress corrosion. The measurement of residual stress is of great significance for ensuring the safety and reliability of workpieces.

At present, there are two main methods for measuring residual stress: mechanical method and physical method. Mechanical methods such as drilling require the destruction of workpieces; Physical methods such as X-ray, magnetic measurement, and ultrasonic testing are all non-destructive testing methods that do not cause damage to the workpiece.

Measurement of residual stress by X-ray diffractionAs a widely used technique, measuring residual stress using X-ray diffraction method is a widely applied technique.

Advantages of X-ray residual stress measurement technology:

1. Widely applicable and currently the mainstream solution for residual stress measurement

2. The measurement results are relatively accurate

Disadvantages of X-ray residual stress measurement method:

1. It takes a long time, usually ranging from a few minutes to a dozen minutes per point;

2. There is a radiation risk

3. Only surface residual stress values can be obtained, and internal residual stress measurement requires removing surface material before measurement

4. Measurement personnel need to receive systematic training for operation

Micro magnetic measurement residual stress methodIt is a method of measuring Barkhausen noise, incremental magnetic permeability, tangential magnetic field harmonic analysis, and multi frequency eddy current using micro magnetic technology to obtain more than 40 parameters, and then obtaining residual stress values through comparative analysis.

Micro magnetic measurement residual stress methodTechnical advantages:

1. Determine the local hardness, hardening layer depth, and residual stress of the component.  

2. Continuously monitor the tensile strength and yield strength of steel strips or plates.

3. Determine the hardness and hardening layer depth of the parts after induction hardening, carburizing, laser and nitriding hardening.

4. Determine the deep drawing performance and residual stress of the steel plate.  

5. Determine the residual stress of assembled components.

6. Timely detect thermal aging, embrittlement, fatigue, and creep damage

7. Can be integrated into the production line

Micro magnetic measurement residual stress methodTechnical drawbacks:

1. Each material requires pre calibration with X-ray residual stress measurement instrument results and establishment of a database

2. Only residual stress values of the surface and shallow layers can be obtained

3. Can only measure ferromagnetic materials

The ultrasonic residual stress measurement method uses longitudinal and transverse wave ultrasonic probes to measure the ultrasonic wave velocity of longitudinal and orthogonal polarized transverse waves, and then calculates and analyzes the residual stress value.

Advantages of ultrasonic residual stress measurement method:

1. The measurement is relatively simple, portable, and radiation free

2. In addition to obtaining the surface residual stress value, the average stress value in the thickness direction can also be obtained

Disadvantages of ultrasonic residual stress measurement method:

1. Each measuring point needs to be measured at least twice

2. The measured value cannot accurately correspond to a certain point, and the stress value corresponds to the average value in a certain direction

3. The accuracy of measurement results is affected by external factors such as coupling agents

4. The measurement surface needs to be in good contact with the probe, smooth and clean, without coating, etc

5. The measurement probe is equipped with a magnetic adsorption or clamping device, which to some extent affects the measurement value

The EMATs electromagnetic ultrasonic residual stress measurement method uses electromagnetic ultrasonic transducers (two linearly polarized horizontal shear waves at 90 ° to each other) to measure the sound velocity of the tested material and analyze the residual stress values.

Technical advantages of EMATs electromagnetic ultrasonic residual stress measurement method:

1. Non contact electromagnetic ultrasound technology

2. Electromagnetic ultrasonic probes do not require mechanical loading onto the surface being measured, achieving higher measurement accuracy with changes in the time of ultrasonic arrival.

3. "Beam control" errors caused by improper bonding between the probe and the surface

4. It has the ability to penetrate surface coatings or corrosion, and may generate scattered or reflected waves from parts outside the component.

5. Portable measurement or online integrated measurement

Disadvantages of EMATs electromagnetic ultrasonic residual stress measurement method:

1. Generally only used for measuring metal materials