Patent ID: 11965861
Assignee: NANJING UNIVERSITY OF AERONAUTICS AND ASTRONAUTICS
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. An equivalent acceleration method of creep loads based on a consistent failure mode, comprising:
S1, obtaining corresponding tensile strengths σbi at different temperatures Ti through high-temperature tensile tests of materials, wherein i=1, 2, 3 . . . , n;
S2, obtaining corresponding creep rupture time tf, rupture strain εf and a minimum creep rate {dot over (ε)}m at different stress temperatures (σi,Ti) through a high temperature creep test of materials;
S3, establishing a rupture time law, a minimum creep rate law and a rupture strain law, and then obtaining a creep damage tolerance factor under a corresponding stress-temperature (σi,Ti) combination;
wherein based on the creep rupture time tf, the rupture strain εf, the minimum creep rate {dot over (ε)}m the tensile strength σb and the temperature T obtained in S2, the rupture time law, σ
    
     σ
     b
    
   
   =
   
    exp
    [
    
     -
     
      
       
        k
        1
       
       [
       
        
         t
         f
        
        *
        
         e
         
          
           Q
           c
           *
          
          
           R
           ⁢
           T
          
         
        
       
       ]
      
      u
     
    
    ]
   
  
  ,
 

 the minimum creep rate law, σ
   
    σ
    b
   
  
  =
  
   exp
   [
   
    -
    
     
      
       k
       2
      
      [
      
       
        
         ε
         .
        
        m
       
       *
       
        e
        
         
          Q
          c
          *
         
         
          R
          ⁢
          T
         
        
       
      
      ]
     
     v
    
   
   ]
  
 

 and the rupture strain law, ε
   f
  
  =
  
   
    
     ε
     fmax
    
    +
    
     
      
       ε
       
        f
        ⁢
        min
       
      
      (
      
       
        
         ε
         .
        
        m
       
       /
       
        
         ε
         .
        
        
         m
         ,
         cr
        
       
      
      )
     
     
      -
      α
     
    
   
   
    1
    +
    
     
      (
      
       
        
         ε
         .
        
        m
       
       /
       
        
         ε
         .
        
        
         m
         ,
         cr
        
       
      
      )
     
     
      -
      α
     
    
   
  
 

 are established, and then the creep damage tolerance factor λ=εf/({dot over (ε)}m*tf) under the corresponding stress-temperature combination (σi,Ti) is obtained;
wherein e is a natural index, k1, k2, u, v, α are fitting parameters, R is a gas constant R=8.314 J/(mol*K), Qc* is creep activation energy, εf max and εf min are a maximum rupture strain and a minimum rupture strain respectively, and {dot over (ε)}m,cr is a median fracture strain, a minimum creep rate value corresponding to, ε
    f
   
   =
   
    
     
      ε
      
       f
       ⁢
       max
      
     
     +
     
      ε
      
       f
       ⁢
       min
      
     
    
    2
   
  
  ;
 

S4, obtaining a creep duration ti of each grade of stress-temperature (σi,Ti) combination through a creep test of materials under variable temperatures and variable loads;
S5, calculating a value of parameter p in a multi-grade variable temperature and variable load creep nonlinear damage accumulation model by combining the tensile strengths σbi at all grades of temperature obtained in S1, rupture time tfi at all grades of stress-temperature (σ,Ti) combination obtained in S2 and the creep duration ti at all grades obtained in S4 based on a multi-grade variable temperature and variable load creep nonlinear damage accumulation model;
wherein the multi-grade variable temperature and variable load creep nonlinear damage accumulation model is:, D
  =
  
   
    
     (
     
      
       
        (
        
         
          
           (
           
            
             
              (
              
               
                t
                1
               
               
                t
                
                 f
                 ⁢
                 1
                
               
              
              )
             
             
              φ
              
               1
               ,
               2
              
             
            
            +
            
             
              t
              2
             
             
              t
              
               f
               ⁢
               2
              
             
            
           
           )
          
          
           φ
           
            2
            ,
            3
           
          
         
         +
         
          
           t
           3
          
          
           t
           
            f
            ⁢
            3
           
          
         
        
        )
       
       
        φ
        
         3
         ,
         4
        
       
      
      +
      …
      +
      
       
        t
        
         n
         ⁢
         1
        
       
       
        t
        
         fn
         -
         1
        
       
      
     
     )
    
    
     φ
     
      
       n
       -
       1
      
      ,
      n
     
    
   
   +
   
    
     t
     n
    
    
     t
     fn
    
   
  
 

wherein, φ
    
     
      n
      -
      1
     
     ,
     n
    
   
   =
   
    
     ln
     ⁡
     (
     
      
       -
       
        ln
        ⁡
        (
        
         
          σ
          n
         
         /
         
          σ
          
           b
           ⁢
           n
          
         
        
        )
       
      
      
       -
       p
      
     
     )
    
    /
    
     ln
     ⁡
     (
     
      
       -
       
        ln
        ⁡
        (
        
         
          σ
          
           n
           -
           1
          
         
         /
         
          σ
          
           
            b
            ⁢
            n
           
           -
           1
          
         
        
        )
       
      
      
       -
       p
      
     
     )
    
   
  
  ;
 

S6, calculating a damage tolerance factor value λ corresponding to each grade of creep load according to the creep damage tolerance factor obtained in S3, and dividing failure mode consistency interval of the creep load with variable temperatures and variable loads according to the damage tolerance factor value λ;
wherein when 1<λ<2.5, the failure mode is a grain boundary cavity, when 2.5<λ<5, the failure mode is necking, and when λ>5 the failure mode is unstable microstructure dominated by coarse precipitates; adjacent creep loads with variable temperatures and variable loads with damage tolerance factors between 1<λ<2.5, 2.5<λ<5, and λ>5 are equivalently accelerated to a maximum creep state of an uniform damage interval, so as to realize a division of the failure mode consistency interval of the creep loads with variable temperatures and variable loads; and
S7, calculating damage caused by the creep load in the failure mode consistency interval respectively by using the multi-grade variable temperature and variable load creep nonlinear damage accumulation model, and accelerating caused damage to a maximum creep load state in the failure mode consistency interval according to a principle of damage equivalence, and finally realizing the equivalent acceleration of creep load.