Introduction to residual stress The equilibrium internal Stress of the self phase in the object after the Residual Stress eliminates the external force or the uneven temperature field. Both mechanical and reinforcement processes can cause residual stress. Such as cold drawing, bending, cutting, rolling, shot blasting, casting, forging, welding and metal heat treatment, etc., may cause residual stress due to non-uniform plastic deformation or phase change. Residual stress is generally harmful, such as the part after improper heat treatment, welding or cutting, the residual stress can cause the part to warp or distort, or even crack. Or after quenching, grinding surface will appear cracks. The existence of residual stress sometimes does not immediately appear as defects, and when the total stress exceeds the strength limit due to the superposition of working stress and residual stress in the work of the part, cracks and fractures will appear. Most of the residual stress of the part can be eliminated by proper heat treatment. Residual stress can also have beneficial aspects and can be controlled to improve the fatigue strength and wear resistance of parts. The existence of residual stress, on the one hand, will reduce the strength of the workpiece, so that the workpiece in the process of manufacturing deformation and cracking defects; On the other hand, it will change the size of the workpiece or reduce its fatigue strength, stress corrosion and other mechanical properties during the natural release process after manufacturing. Therefore, the measurement of residual stress is very important to ensure the safety and reliability of the workpiece.

Application field:

Development of residual stress measurement techniques

• The residual stress testing methods are mainly divided into two categories: one is the mechanical release measurement method with certain damage, that is, the residual stress is released and measured by local failure of components, such as the stress release method and the blind hole method. Second, the method of physical measurement without damage, such as X-ray method, ultrasonic method, photoelastic method, magnetic measurement method. Magnetic measurement is a method to determine the magnitude and direction of residual stress through the change of magnetic permeability caused by ferromagnetic materials under the action of force. Magnetic measurement method has the advantages of portable instrument, simple operation, fast measurement speed and strong adaptability. Mastering and developing this technology is of great practical significance to industrial production and scientific research.
• In the 1960s, Japan, Germany, the former Soviet union and other countries carried out a lot of research on the residual stress of magnetic measurement method, and made abundant achievements. To this day, this method is still one of the most important methods for residual stress testing.
• The application of magnetic residual stress in China has never ceased. From the analysis of the residual stress of liquefied petroleum gas spherical tank, the research of the internal residual stress testing technology of plate components, the research of the residual stress of welding joints, the research of the residual stress of automobile spring steel plate, the research of the residual stress of ship welding to the stress testing system of high-speed railway wheels, the research of the residual stress of landing gear of fighter plane, etc.

The advantage of sex method in measuring residual stress:

• Completely non-destructive, no damage to the workpiece;
• Rapid detection speed, easy to carry;
  It can improve the frequency of sampling inspection, so as to ensure timely adjustment of the process and improve the stability of the product.
• Simple operation, good reproducibility and reproducibility of detection results, and computer software storage results, easy to call at any time to see.

Three-dimensional residual stress testing system

Test conditions:

• Suitable for steel, cast iron and other ferromagnetic materials
• No dirt, oil film and oxide layer on the surface
• No strong electromagnetic interference within 3m.

Parameters of the residual stress tester MRS-PLUS:

• Measuring frequency range: adjustable
• Single point test time is less than 2m
• The sensitivity: ＞10μA／MPa
• Repeated measurement error: ≤ ±25MPa
• Power supply:AC220±5％，50Hz±2％
• power≤100W
• Weight:5.00 Kg
• Sensor size:standardφ16ｍｍ(customizable)

Other features:

• Instruments can be used with automation equipment (optional)
• Easy to use and mobile to use
• Software can be customized according to customer requirements (optional)
• On-line inspection

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Comparison of magnetic and X-ray applications:

Typical customers

AITTEST^®

AITTEST provides users and research partners with a full range of non-destructive testing technologies, both in the field of basic research and applied research. Our researchers, engineers, and technicians work on the development of modern automated intelligent test applications, including feasibility studies, consulting, training and inspection services, and the creation of system prototypes.

• As an international leading research and development center in the field of (MTT) technology, AITTEST focuses on:
  Innovation of nondestructive testing technology
  Deep research on magnetic technique
  Development of automation and intelligent testing technology
  Automation plant upgrade
• Application-oriented solutions cover the entire value chain with the aim of strengthening the competitive position of industry partners at the domestic and international levels.

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