When combining the results of crack length
measurement and the manual measurements of the crack width at the reference points, it is possible to calculate the width below which the end of a crack cannot be detected.
Literature offers more detailed formulas of [eta]-factor calculation at various crack length
including deep and shallow cracks.
For each crack length
, the central frequency of excitation was varied from 15 to 60 kHz.
0] is the critical deflection corresponding to crack initiation, D is the maximum deflection in the bending process, L is the crack length
in one half of the sample, [E.
A curve is drawn depends on the length of crack (a), this length was determined using a method, in witch the value of crack length
was determined by processing images captured with the JVC camera using software Irfan View.
The method is based on determination of a crack length
, occurring in the material around an imprint in indentation of the diamond pyramid according to Vickers method at a low load.
where [alpha]--is the ratio of the crack length
a to the specimens width W.
S], where D is the average crack length
(in any direction) and [D.
Measurements of crack length
from both specimen's edges during the loading history (Fig.
da) is the crack length
increase (a) as a function of cycle number (dN).
Occasionally, data will be obtained which show a distinct waviness in the plot of crack length
P = Load, B = Specimen thickness, W = Specimen length, a = Initial crack length