**4.2 Application of this theory to the case of a smooth specimen and a notched specimen**

The *QL*\* map of a double edge notched and a smooth specimen for Cr-Mo-V steel is shown in **Figure 16**.

These results showed that the *QL*\* line of the smooth specimen is parallel to and lower of Δ*QL*<sup>∗</sup> than that of the notched specimen [12]. Therefore, one creep fracture test of the short range life is necessary to determine the value of Δ*QL*<sup>∗</sup> , after that, as shown in **Figure 17**, the converted stress of the smooth specimen in to the applied stress of the notched specimen and its ratio, η are feasible to obtain according to the flow chart given by **Figure 5**.

## **5. Summary**

The experimental law on the relationship between the steady state creep rate and creep fracture life given by Eq. (21) was well known as the Monkman – Grant law [19], however, Yokobori, et al. showed this law is only valid under limited case, and the data band is essentially different depending on the creep ductility as shown in **Figure 3** [11].

Furthermore, however the similar equation as Eq. (21) was found to be valid for creep ductile materials and it was correctly written by Eq. (8).

$$\mathbf{t}\_f \times \dot{\mathbf{e}}\_s = \text{Const.} \tag{21}$$

**Figure 16.**

*QL\*map of a notched specimen and a smooth specimen for the Cr-Mo-V steel [12]. DEN: a double edge notched specimen of a plate specimen. CT: a C (T)specimen. Open mark: steady state creep rate. Solid mark: remnant life of creep fracture for the current creep rate. Experimental data of solid mark exist on the same QL\* line and the QL\* line of the notched specimen is parallel to that of smooth specimen.*

**Figure 17.**

*The prediction method of creep fracture life and the converted stress of the applied stress of a smooth specimen into that of a notched specimen.*

In this study, for creep ductile materials, *QL\** line was found to be written by Eq. (8) and its parallel lines of a notched and a smooth specimen for the base metal and the weld joint.

On the basis of these results mentioned above, the prediction of the creep fracture life and the quantitative estimation of the MPCS were found to be possible using the *QL\** map and the concept of converted stress, with the short experimental period, the small number of specimens, the reasonable accuracy and an economic efficiency. It is significant from engineering point.

*The Quantitative Estimation of Mechanical Performance on the Creep Strength… DOI: http://dx.doi.org/10.5772/intechopen.106419*

The experimental data obtained by the commissioned research with Tohoku Electric Power Co.Inc. from April 2016 to March 2019 were used in the section of 3.3 in this proof [20].
