Fracture is largely determined by the fracture toughness (
  
    
      
        
          
            K
          
          
            
              c
            
          
        
      
    
    {\textstyle \mathrm {K} _{\mathrm {c} }}
  ), so fracture testing is often done to determine this. The two most widely used techniques for determining fracture toughness are the Three-point flexural test and the compact tension test.
This is done by taking the test piece with its fabricated notch of length 
  
    
      
        
          c
          ′
        
      
    
    {\textstyle \mathrm {c\prime } }
   and sharpening this notch to better emulate a crack tip found in real-world materials. Cyclical prestressing the sample can then induce a fatigue crack which extends the crack from the fabricated notch length of 
  
    
      
        
          c
          ′
        
      
    
    {\textstyle \mathrm {c\prime } }
    to 
  
    
      
        
          c
        
      
    
    {\textstyle \mathrm {c} }
  .