Issue 62

Yu. G. Matvienko et alii, Frattura ed Integrità Strutturale, 62 (2022) 541-560; DOI: 10.3221/IGF-ESIS.62.37



   

       0, 0 m m D N k ,

Cr

 m m F D N N k ,



.

(6)

1

Cr

 m F N N that corresponds to short crack appearance at

 1 m D in relationships (6) is related to

The second limiting case

the external specimen face. A capability to reveal loading cycle number that corresponds to surface macro-defect arising and obtaining required value of chosen deformation parameter is a remarkable feature of the proposed non-destructive approach. This is evident advantage over the destructive technique based on the narrow notch inserting and further fracture mechanics parameters determination, which involves complete separations of the specimen by two fragments as the second limit case [40–42, 45]. An explicit form of the function      Ψ , k m N k from Eqns. (4) and (5) can be presented as:

     S k k N k D



   , 0





 

m

k



 N k ,

Ψ

(7)



m

Cr



, k N N

m

F

 

k D S k is normalizing coefficient that must be derived from the experimental  , m k N is a set of experimental values of damage indicator, obtained after is a value of chosen damage indicator that corresponds to maximum level of tensile m F N N means loading cycle number that corresponds to short crack appearance at   Cr

where m N is current number of loading cycle; data for each specific damage indicator; 

m N cycles;  





, m k N

0

reaching

remote stress for the first half cycle;

the external specimen face. Substitution of the function



   

k

, m N k

Ψ

from Eqn. (7) into relationship (5) and summarizing along the segments

    1 m m m N N N , at end points of which values of chosen damage indicator    , of integration, gives the explicit form of the damage accumulation function:

m k N have been determined instead

     S k k N , k



Cr







  m F m 0

N N

  D N k  , m m

D

m



(8)





    0 Cr k N N N ,



N

m

F

m

where     1 m m m N N N denotes number of loading cycles between two neighbouring points of    , m k N determination.

Figure 10: Evolution of normalized deformation parameters   

   

  2 A MAX x

   1 A

 0 m N to

x and

in the range from

 Cr m F N N .

554