Method for processing welded metal work joints by high-frequency hummering

Abstract

The inventive method relates to reinforcing treatment of welded metalwork joints using a power ultrasound. Said method can be used for mechanical engineering, shipbuilding, bridge engineering and other branches of industry and construction producing welded structures which can be safely used at conditions of static, dynamic and repeated-variable loading. The inventive method consists in specifying the method for calculating normalised residual compressive stresses to be produced by an ultrasound impact processing. Said stresses are related to the geometrical dimensions of a groove formed when the area disposed along a line between the joint and a base metal is treated. Said invention makes it possible to maximally increase the fatigue limit and the cyclic life duration of welded joints.

1 . A method of improvement treatment of welded joints of metallic structures by high-frequency peening that uses the effect of application of an ultrasonic impact device with determined oscillation amplitude of the horn tip in the zone of the weld. The proposed method differs from other ones by followings parameters: the treatment is performed in stress concentration zones of welds which are located along the transition line from weld to base metal—weld toe, by inducing the predetermined level of compressive residual stresses σ res   ls  providing that the minimum cyclic stresses in the stress concentration zone during the loading reach the yield stress of the material σ Y . The required value of σ res   ls  is calculated, depending on the stress ratio, the type of welded joint, the stress concentration factor and the mechanical properties of the material, by using the following expression:  
       
         
           
             
               
                 
                   σ 
                   res 
                   ls 
                 
                 = 
                 
                   { 
                   
                     
                       σ 
                       Y 
                     
                     + 
                     
                       
                         2 
                          
                         
                             
                         
                          
                         
                           α 
                           σ 
                         
                          
                         
                           
                             R 
                             σ 
                           
                            
                           
                             ( 
                             
                               
                                 σ 
                                 S 
                               
                               + 
                               
                                 
                                   σ 
                                   Y 
                                 
                                 
                                   α 
                                   σ 
                                 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           ( 
                           
                             1 
                             - 
                             
                               R 
                               σ 
                             
                           
                           ) 
                         
                         [ 
                         
                           
                             
                               ( 
                               
                                 
                                   σ 
                                   S 
                                 
                                 - 
                                 
                                   
                                     σ 
                                     Y 
                                   
                                   
                                     α 
                                     σ 
                                   
                                 
                               
                               ) 
                             
                             
                               σ 
                               a 
                               l 
                             
                           
                           + 
                           2 
                         
                         ] 
                       
                     
                   
                   } 
                 
               
               , 
             
           
           
           
               
           
         
       
       where, σ res   ls  is the normalized compressive residual stress at which the minimum cyclic stresses from external loading in the stress concentration zone achieve the yield strength of the material; σ Y  is the yield strength of the material, σ S  is the ultimate strength of the material; α σ  is the stress concentration factor; R σ  is the stress ratio; σ α   n  is the limit stress amplitude of welded joint in as-welded condition with high tensile residual stresses  
     
     
         2 . A method as described in  claim 1  that differs by the fact that in welded structures made from steel and alloys of different strength during the high-frequency peening due to plastic deformation of metal the groove of width 2-7 mm and depth 0.2-1 mm is formed, with the geometrical parameters that depend on treatment parameters and are connected with the value of σ res   ls  for selected material and type of welded element.