By this method the elasticity theory is used to model an inelastic material. Fung has called this model as pseudoelastic to point out that the material is not truly elastic. Residual stress
In physiological state soft tissues usually present residual stress that may be released when the tissue is excised. Physiologists and histologists must be aware of this fact to avoid mistakes when analyzing excised tissues. This retraction usually causes a visual artifact.
This written in respect of the principal stretches (
  
    
      
        
          λ
          
            i
          
        
      
    
    {\displaystyle \lambda _{i}}
  ):

  
    
      
        W
        =
        
          
            1
            2
          
        
        
          [
          
            a
            (
            
              λ
              
                1
              
              
                2
              
            
            +
            
              λ
              
                2
              
              
                2
              
            
            +
            
              λ
              
                3
              
              
                2
              
            
            −
            3
            )
            +
            b
            
              (
              
                
                  e
                  
                    c
                    (
                    
                      λ
                      
                        1
                      
                      
                        2
                      
                    
                    +
                    
                      λ
                      
                        2
                      
                      
                        2
                      
                    
                    +
                    
                      λ
                      
                        3
                      
                      
                        2
                      
                    
                    −
                    3
                    )
                  
                
                −
                1
              
              )
            
          
          ]
        
      
    
    {\displaystyle W={\frac {1}{2}}\left[a(\lambda _{1}^{2}+\lambda _{2}^{2}+\lambda _{3}^{2}-3)+b\left(e^{c(\lambda _{1}^{2}+\lambda _{2}^{2}+\lambda _{3}^{2}-3)}-1\right)\right]}
   ,where a, b and c are constants.