Abstract
Ultrasonic peening treatment (UPT) as a method of severe plastic deformation was used to treat cruciform welded joints of Q345 steel. The application of UPT achieves material surface nanocrystallization of the peening zone, reduces stress concentration, and produces residual compressive stresses at the welded toe. Micro-structure, hardness, stress relief, S-N curve, and the fatigue fracture mechanism of cruciform welded joint of Q345 steel, both before and after UPT, were analyzed in detail. The main results show that: stress concentration and residual tensile stress are the main reasons to reduce fatigue strength of cruciform welded joints. The fatigue life of cruciform welded joints is improved for surface hardening, compressive stress, and grain refinement by UPT. Residual compressive stress caused by UPT is released with the increase of fatigue life. A very significant fatigue strength improvement happens when UPT is replenished repeatedly after a certain number of cycles.
Highlights
Welding has been widely used in many aspects of industrial production as a main method of connecting mechanical parts
For the welded joints with Ultrasonic peening treatment (UPT) reapplications, the weld toe always maintained during the residual compressive stress, fatigue fracturing has not occurred at the weld toe, and instead another weak point of the sample has become the position of crack initiation
Stress concentration and residual tensile stress are the main reasonson to the reduce fatigueofstrength
Summary
Welding has been widely used in many aspects of industrial production as a main method of connecting mechanical parts. It is well established that fatigue strength of welded joints can be enhanced by producing compressive residual stress, reducing stress concentration, increasing hardness, and forming nanocrystalline structures. Dressing, common hammering, weld toe grinding, a spraying method, shot peening, and so on [4,5,6,7,8]. The spraying method can effectively reduce stress concentration and improve surface properties, but the bonding strength between the layer and the matrix is weaker, and a fatigue crack can form at the bonding position under the high stress level [12]. The improvement of fatigue life for a cruciform welded joint still cannot depend a cruciform welded joint still cannot depend entirely on shot peening. The effect of residual performance of cruciform welded joints of Q345 steel will be studied.
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