Comparison of RT and 150°C strengths subjected to static or fatigue loading

To examine the high-temperature performance of the material tested, we will discuss the ratio of 150°C strength to RT strength when the specimens are subjected to either static or fatigue loading. This strength ratio, r150(N), is defined as

r150(N) , 150°Cstrength(N) (4)

RT strength (N)

where static strength is given for N=1.

Table 6 indicates r150(N) values calculated by Eq. (4) for NH and OH specimens. Since the static strength ratio was described in Section 3.1, this section gives only numerical values in Table 6 for the sake of comparison. In the case of fatigue strength, the ratio was calculated by the S-N equation, Eq. (2), and the parameters in Table 4. For OH specimens the 150°C fatigue strength is adequately high in comparison with RT fatigue strength. In addition, the ratio of OHT fatigue strength agrees with that of OHT static strength. Furthermore, the ratio for OHC fatigue strength is larger than that for OHC static strength, i. e., the reduction in fatigue strength is smaller than that in static strength. This result is remarkable. Moreover, the tension-compression fatigue strength of OH specimens was adequately high at 150°C in comparison with that at RT.

As mentioned above, a high ratio listed in Table 6 for static and fatigue strengths indicates the high temperature performance of the material tested, and can be evaluated to demonstrate sufficient practical utility from the viewpoint of static and fatigue strength at 150°C.

Specimen and loading

Static strength ratio, Г150(1)

Fatigue strength ratio, r150(N)

N=104

N=105

N=106

N=107

NH tension

90 %

NH compression

75 %

OH tension

97 %

97 %

97 %

97 %

97 %

OH compression

84 %

88 %

90 %

93 %

97 %

OH tension – compression

88 %

89 %

90 %

92 %

Table 6. The ratio of strength at 150°C to that at RT, r150(N), for NH and OH specimens given by the mean static strength and the fatigue strength calculated from the Smax-N equation