Data Reduction

In this research, creep compliance is calculated as a function of horizontal deformations. A detailed review of the measurement and analysis system is pre­sented in Ref 18. All correction factors are considered to depend on Poisson’s ra­tio. With this adjustment, the creep compliance was obtained as follows:

1.071 • Cbx

D(t)=-2^—————————- (2)

(Csx + 3v. Csy)

nwd

where D(t) = creep compliance, 1/GPa; v = Poisson’s ratio; P = creep load, N; CBX = horizontal bulging correction factor; CSX = horizontal stress correction factor; CSY = vertical stress correction factor; D = diameter of the specimen, mm; LG = length between gauge point centers, mm; W = thickness of the speci­men, mm; and HTRIM (t) = trimmed average horizontal deformation, mm.

The trimmed average horizontal deformation is calculated by ranking each of the horizontal arrays according to their deflection values in considering a window around the middle of the test (46-50 s). After ranking, the horizontal deflection with the highest and the lowest measurement values are removed from the data analysis and four of these results are used out of the six measure­ments to determine the creep compliance; for details see Ref 18. Creep compli­ance is calculated with Eq 2. from the row data of IDT for three different temperatures (5 °C, 15 °C, and 25 °C) as indicated in Table 1.