AN ALTERNATIVE ANALYTICAL APPROXIMATION OF THE <i>C</i><sub>t</sub> PARAMETER

Adefris,; McDowell,; Saxena,

doi:10.1046/j.1460-2695.1998.00531.x

Cited by 8 publications

(7 citation statements)

References 14 publications

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“…We speculate that this is due to the creep deformation that occurs during the hold time and is not fully reversed (or the creep reversal is incomplete) by plastic deformation during unloading portion of the cycle. To account for this, we invoke the creep reversal parameter, C R , described as follows.…”

Section: Inclusion Of Crack Tip Cyclic Plasticity In the Estimation Omentioning

confidence: 91%

“…Figure 5 shows a consolidated plot of all 60-and 600second hold time data along with creep crack growth rate (CCGR) data. In earlier studies on 1.25 Cr-0.5 Mo (ASTM Grade P11) steels, 2.25 Cr-1Mo (ASTM Grade P22) steels, and 1Cr-1Mo-0.25 V rotor steels (ASTM A470 Class 8), [4][5][6] the (da/dt) avg versus (C t ) avg data were found to be independent of the hold time. The trend in Figure 5 shows a similar trend between 600-second hold time and the CCG behavior but the 60-second hold time data showed slower crack growth rates than the 600-second hold time data and the CCG rates.…”

Section: Accounting For Incomplete Creep Strain Reversal During Unloa...mentioning

confidence: 99%

“…First, the stress‐intensity parameter is given by Equation below:

K = \frac{P}{{(B B_{N})}^{\frac{1}{2}} W^{\frac{1}{2}}} F ((), \frac{a}{W}),

where

F ((), \frac{a}{W})

is given by the following:

F ((), \frac{a}{W}) = ([], \frac{2 + \frac{a}{W}}{{(1 - \frac{a}{W})}^{3 / 2}}) ((), 0.886 + 4.64 ((), \frac{a}{W}) - 13.32 {(\frac{true}{a})}^{2} + 14.72 {(\frac{true}{a})}^{3} - 5.6 {(\frac{true}{a})}^{4}) .

Previous studies performed on creep‐ductile power plant materials using C(T) specimens have shown ( C t ) avg to be the most effective crack tip parameter in correlating creep‐fatigue crack growth rates in these materials for trapezoidal wave form with a hold time, t h . In such cases, the time dependent crack growth, ( da / dt ) avg , during the hold period is expressed as a function of the average magnitude of the C t parameter,( C t ) avg , defined as follows:

{(C_{t})}_{avg} = \frac{1}{t_{h}} \int_{0}^{t_{h}} C_{t} italicdt .

( C t ) avg is estimated from the following equation for test specimens in which both force and force‐line deflection behavior with time are measured:

{(C_{t})}_{avg} = \frac{italicΔP {ΔV}_{c}}{{(B B_{N})}^{<...>}}

…”

Section: Introductionmentioning

confidence: 99%

“…The first term on the right-hand side of the Equation ( 6) represents the small-scale creep contribution and the second term represents the extensive creep contribution to the value of (C t ) avg . The function h 1 (a/W,n) for various a/W and n are available from Kumar et al 8 Under the domination of small-scale-creep conditions, the contribution of C * will be negligible in comparison with the first term on the right-hand side of Equation (6).…”

Section: Introductionmentioning

confidence: 99%

“…(C t ) avg is estimated from the following equation for test specimens in which both force and force-line deflection behavior with time are measured 1,2,[5][6][7] :…”

Section: Introductionmentioning

confidence: 99%

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Accounting for crack tip cyclic plasticity and creep reversal in estimating (C_t)_avg during creep‐fatigue crack growth

Saxena

Narasimhachary

2019

Fatigue Fract Eng Mat Struct

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Creep‐fatigue crack growth (C‐FCG) rates in a P91 steel at 625°C were correlated as the average time rate of crack growth during hold time, (da/dt)avg, with (Ct)avg. At 60‐second hold time, the rates were lower than for 600‐second hold time. At 600‐second hold time, the crack growth rates converged on to the creep crack growth rate (CCGR) trend. Thus, the CCGR trend represents the upper bound for time‐dependent crack growth rates in P91 materials. The analytical expressions based on considering just the elastic and secondary creep deformation rates overestimated the magnitudes of (Ct)avg by as much as a factor of 10 for the 600‐second hold time tests. After accounting for the effects of cyclic plasticity during unloading, and accounting for only partial reversal of creep strains accumulated during hold time, the estimates of (Ct)avg compared well with the measured values. CR represents the extent of crack tip creep strain reversal, and tpl is the time required for the crack tip creep zone during the hold time to become equivalent in size to the cyclic plastic zone in terms of stress carried by that region. Together, these parameters accurately account for the effects of crack tip cyclic plasticity on the magnitude of (Ct)avg. Both tpl and CR depend on material properties, and the latter also depends on the hold time. A parameter ϕ is introduced that is dependent only on material properties and from which CR can be estimated for a given hold time. tpl and ϕ can be reported as part of the test results from C‐FCG testing.

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Section: Inclusion Of Crack Tip Cyclic Plasticity In the Estimation Omentioning

confidence: 91%

Section: Accounting For Incomplete Creep Strain Reversal During Unloa...mentioning

confidence: 99%

“…First, the stress‐intensity parameter is given by Equation below:

K = \frac{P}{{(B B_{N})}^{\frac{1}{2}} W^{\frac{1}{2}}} F ((), \frac{a}{W}),

where

F ((), \frac{a}{W})

is given by the following:

F ((), \frac{a}{W}) = ([], \frac{2 + \frac{a}{W}}{{(1 - \frac{a}{W})}^{3 / 2}}) ((), 0.886 + 4.64 ((), \frac{a}{W}) - 13.32 {(\frac{true}{a})}^{2} + 14.72 {(\frac{true}{a})}^{3} - 5.6 {(\frac{true}{a})}^{4}) .

{(C_{t})}_{avg} = \frac{1}{t_{h}} \int_{0}^{t_{h}} C_{t} italicdt .

( C t ) avg is estimated from the following equation for test specimens in which both force and force‐line deflection behavior with time are measured:

{(C_{t})}_{avg} = \frac{italicΔP {ΔV}_{c}}{{(B B_{N})}^{<...>}}

…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…(C t ) avg is estimated from the following equation for test specimens in which both force and force-line deflection behavior with time are measured 1,2,[5][6][7] :…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations