Patent ID: 11927563
Assignee: NANJING UNIVERSITY
Field: Measurement (Instruments)
Classification: CPC G  B  H | IPC B  G  H

Claim 1:
2. The method according to claim 1, wherein in the step S1), further comprises:
controlling the tip of the ultrasonic impact gun to perform impact treatment on the postwelding seam with different treatment pressures, treatment speeds, treatment angles and impact frequencies; and acquiring acoustic signals in the impact treatment process;
Fourier transform is used to transform the acoustic signals in a time domain into acoustic signals in a frequency domain, and a Butterworth filter is used to filter the acoustic signals in the frequency domain;
after being filtered, the acoustic signals are framed to extract short-time features;
a short-time windowing technology is adopted for framing; a Hamming window is adopted, the length of which is 1024, and framing is conducted based on an overlapping rate of 50%;
then, the short-time zero-crossing rate, short-time average amplitude, short-time energy and short-time zero-energy ratio of the acoustic signals can be extracted from the time domain;
(1) short-time zero-crossing rate:
short-time zero-crossing rate refers to number of times the signal passes through the zero value in a frame of signals; formula for calculating the short-time zero-crossing rate Zn is as follows:, Z
    n
  
  =
  
    
      1
      2
    
    ⁢
    
      
        ∑
        
          m
          =
          n
        
        
          n
          +
          N
          +
          1
        
      
      ⁢
      
        
        
          sgn
          ⁡
          
            [
            
              
                
                  x
                  ω
                
                ⁡
                
                  (
                  m
                  )
                
              
              -
              
                sgn
                ⁡
                
                  (
                  
                    
                      x
                      ω
                    
                    ⁡
                    
                      (
                      
                        m
                        -
                        1
                      
                      )
                    
                  
                  )
                
              
            
            ]
          
        
        
      
    
  

where n represents the current sampling time point, N is the length of the Hamming window, xω(m) represents the windowed signal of x(m), and x(m) is the amplitude of the acoustic signal at time m;
(2) short-time energy:
under different variables, there is a significant energy difference between acoustic signals generated by seam impacting with the ultrasonic impact gun;
a formula for calculating the short-time energy En is as follows:, E
    n
  
  =
  
    
      ∑
      
        m
        =
        n
      
      
        n
        +
        N
        -
        1
      
    
    ⁢
    
      
    
    ⁢
    
      
        x
        ω
        2
      
      ⁡
      
        (
        m
        )
      
    
  

(3) short-time average amplitude:
short-time energy refers to sum of squares of acoustic signals in a frame of signals, and short-time average amplitude Mn is used to calculate sum of absolute values to measure a variation amplitude of the acoustic signals; a formula for calculating the short-time energy Mn is as follows:, M
    n
  
  =
  
    
      ∑
      
        m
        =
        n
      
      
        n
        +
        N
        -
        1
      
    
    ⁢
    
      
      
        
          x
          ω
        
        ⁡
        
          (
          m
          )
        
      
      
    
  

(4) short-time zero-energy ratio
short-time zero-energy ratio is the ratio of zero-crossing rate and short-time energy in a frame of signals; the formula for calculating the short-time zero-energy ratio ZERn is as follows:

ZERn=Zn/En.