A review of a time-dependent fracture life law (or model) based on a proposed multi-scale analysis

Abstract

To solve the problem of structural safety under time-dependent fracture conditions, an algorithm of multi-scale hybrid mechanics from the nano-scale to the macro-scales is described. The paper presents an algorithm that links the physics of materials with life prediction determined by creep crack growth and addresses practical application which enables "prediction of fracture" to be developed from "the science of clarification of fracture mechanism" on the basis of the algorithm. In particular, in order to predict the fracture life of real components, the importance of the link between void mechanics caused by vacancy diffusion (micro mechanical factor), the stress tri-axiality, TF (a structural mechanical factor), and the material structure (a meso-mechanical factor) is shown in the proposed formulation for the activation energy of the thermally activated process of creep crack growth. A detailed discussion on these issues as well as on the algorithm relevant to the establishment of the law of creep crack growth life based on the multi-scale analysis is included ranging from the scale of micro damage to structural brittleness.

Theory of particle transport phenomena during fatigue and time-dependent fracture of materials based on mesoscale dynamics and their practical applications

“…Figure 10 62) shows the results of the comparison between the area of vacancy concentration around the notch tip obtained by analyzing the vacancy diffusion given by Eq. [13] and that of creep damage composed of grain boundary micro-cracks observed by the proposed in situ creep-fatigue testing machine. 64) The material was a TiAl intermetallic compound.…”

“…53) Furthermore, as nanoscale vacancy diffusion of creep is driven by hydrostatic stress, 61),62) < P similar to the hydrogen diffusion of hydrogen embrittlement, the vacancy diffusion equation is also given by Eq. [13]. 61),62) However, the material constants and values of , i differ from those of hydrogen diffusion.…”

“…On the basis of this concept and our proposed mesoscale mechanics, new mechanical indexes are derived as dominant factors for predicting fatigue crack growth life 15), 16) and the time-dependent fracture life of notched specimens subjected to hydrogen embrittlement 14) and high-temperature creep. 13) Furthermore, as the blood vessel wall is a viscoelastic material dominated by a time-dependent mechanism (creep mechanism) and is influenced by cyclic pulsatile blood pressure (fatigue effect), it is considered closely related to both fatigue and creep components. As a practical application, our theories were applied for estimating the degree of viscoelastic deterioration and chaotic motion of blood vessel walls, which are closely related to blood vessel diseases such as atherosclerosis and aneurysm, and new indexes to diagnose them were proposed for clinical application.…”

“…38) However, at that time, non-numerical methods for the derivation of an analytical solution were proposed, and the specification of , i in the linear combination of each term of the hydrogen flux J and hydrogen diffusion equations, given by Eqs. [12] and [13], respectively, were taken as unity. 38),39) However, as shown in Eqs.…”

“…36),44) However, if the effect of , i on Eq. [13] is neglected, that is, the value of , i is taken as unity, homogeneous hydrogen diffusion occurs and the time-sequential decreasing behavior of hydrogen concentration appears as shown in Fig. 5(c) 36) ; in particular, hydrogen concentration at the site of maximum hydrostatic stress does not occur even for a yield stress of 1442 MPa.…”