Response of Crack Propagation to Load Variation in Delayed Failure of Ni-Cr-Mo Steels

Crack Propagation Assisted with Hydrogen under Cyclic Stress in Ni–Cr–Mo Steel

“…Thus, from eqs. (7), (8) and (10) (11) On the other hand, the total energy per one cycle (mean value of vibration energy) E without delay of phase is (12) Therefore, the internal friction I.F. is expressed as (13) 2.…”

“…8(a) will be able to represent the relation between stress and strain at a crack tip where hydrogen embrittlement actually occurs. According to the elastic stress field analysis at a crack tip, the hydrostatic (or triaxial) tensile stress at a crack spring-dashpot model is an indication expressing the concentration speed of hydrogen atoms to the triaxially stressed position during a quick increase or decrease in K, being closely connected with the incubation time for crack propagation tu and td(6)(8) (12). Thus, the spring-dashpot model is expected to well represent the response of strain at a crack tip associated with the interaction between hydrogen atoms and the cyclic movement of triaxially stressed position.…”

“…Qd is about twice as large as Qu. The reason for such a large difference between both activation energies may be attributed to a large difference in stress fields at a crack tip occurring depending on whether K increases or decreases (12). Therefore, by assuming that in any case the difference between Qu and Qd becomes larger energy is expressed as follows: Since it is difficult to determine f(R) and g(R) accurately, the following simple forms are assumed in the present study:…”