Ultrasonic impact technology is a new technology developed in recent years. It has a significant effect on improving the fatigue strength of joints after welding, prolonging fatigue life and preventing weld cracking. 1. The basic principle of ultrasonic impact technology In the manufacture of ordinary welded structures, the method of fusion welding is generally used. In most cases, a certain amount of metal is filled, so that there are residual heights, pits and various welding defects at the joints, resulting in severe stress concentration: Certain welding residual tensile stress. In most cases, residual stress is detrimental to the fatigue strength of the welded structure. Under the combined action of stress concentration and welding residual tensile stress, the fatigue strength of the joint is seriously reduced. Ultrasonic impact equipment mainly consists of two parts: power ultrasonic generator and impact mechanism. The basic principle of ultrasonic impact is: after welding, the impact head is used to push the impact joint to impact the joint part, so that it produces large compressive deformation and produces a smooth transition arc. Thereby reducing stress concentration. And it produces a high value of residual compressive stress at the impacted part: and strengthens the surface of the material, thereby greatly improving the fatigue strength of the welded joint. 2. Introduction of Sutong Bridge Sutong Bridge is located in the southeast of Jiangsu Province, connecting Nantong and Suzhou. The estimated total investment is 6.45 billion yuan, and the project construction period is 6 years, with a total length of 32.4 kilometers. The bridge is expected to be completed by the end of 2008. The huge Sutong Bridge is a project with independent intellectual property rights, and it has created the largest main span, the deepest foundation, and the longest cable. The world is the largest in the world. An important symbol of the transformation of bridge manufacturing powers. The formal application of ultrasonic impact technology on the Sutong Bridge not only explains the owner's recognition of the technology, but also increases the guarantee for the construction of the bridge. 3. Basic parameters of ultrasonic impact equipment The process is applicable to the impact welding of the welded joints on both sides of the transverse box and the top elevation weld of the steel box girder of the main bridge of the Sutong Bridge. 1, the impact site The impact area of ​​the transverse diaphragm and the top plate elevation weld is shown in the figure below. 2 The impact angle hammer head is aligned with the welding line, and the angle between the hammer head and the board surface is 60-70 degrees. Place the impact gun vertically in the weld toe area, just give him a force to keep it vertical, without extra force. When impacting, do a small range of reciprocating motion, the hammer moves at an optimum speed of 0.5-1 meters per minute, at a constant speed, and each step is reciprocated 4 times. 4 impact depth Impact depth is 0.1-0.2MM Ultrasonic impact treatment effect judgment: After the impact is completed, the impact area should be inspected. Bright, smooth, straight concave arc grooves shall be observed by visual inspection of the impact toe and weld line. Generally speaking, as long as it can hit the part, it has a good general performance guarantee effect. If there is a leaking area, the area can be compensated. In the actual process, several standard samples of the effect after impact treatment can be prefabricated, so that the inspectors can check and check in the unskilled situation. references: 1. Wang Dongpo, Huo Lixing, Zhang Yufeng, Jing Hongyang, Yang Xinqi. Experimental study on improving the fatigue strength of welded joints by ultrasonic impact method.
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4. Application Specifications of Ultrasonic Impact Technology in Sutong Bridge 
The impact area is the welded joint location of the transverse baffle and the top plate and the V-rib and transverse cross-weld welds within 50MM from the top plate. 
3 impact method and work efficiency 
5. Acceptance Criteria
Ultrasonic impact technology is an effective method to improve the fatigue strength of joints after welding. It has a wider application prospect in the actual production of steel structures.
2. Ultrasonic impact process specification for manufacturing welds of steel box girder of main bridge of Caodongwei Sutong Bridge