This project will investigate the physical aspects of improving the fatigue performance (strength) of high-strength steel welded joints, such as for the use in construction equipment, transportation vehicles and lifting devices, in order to obtain significant weight reduction and improved service life. The samples will be manufactured from plate thicknesses of 6 mm with yield strengths of 355 and 690 MPa. We will examine the well-known fatigue strength improvement technique called high frequency mechanical impact (HFMI) treatment method. Experimental measurements at ISIS will allow mapping the physical characterization and determining residual stress of the welds through the plate thickness. We will develop analytical procedures to assess the benefits and limitations of the treatment method.