Crack Growth Rate Model under Constant Cyclic Loading and Effect of Different Singularity Fields

Crack growth rate experiments are conducted by applying an intermediate single overload cycle in constant amplitude load (CAL) tests. For a particular overload ratio, three to four tests are conducted by applying the overload cycle at different crack lengths. The loads are selected in such a way that for a given overload ratio, the size of the overload and CAL monotonic plastic zones are the same at each crack length. A functional form for the crack growth during the retardation was developed that accurately describes all the tests. For comparison, the corresponding CA-load tests are also conducted separately. Finally, a crack growth rate model is developed.

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Testing method for the determination of the crack growth rate and crack growth resistance under cyclic loading

Materials Science ◽

10.1007/bf00558850 ◽

1995 ◽

Vol 30 (4) ◽

pp. 512-529 ◽

Cited By ~ 2

Author(s):

S. Ya. Yarema

Keyword(s):

Growth Rate ◽

Cyclic Loading ◽

Crack Growth Rate ◽

Crack Growth ◽

Crack Growth Resistance ◽

Testing Method

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Fatigue crack growth rate model for metallic alloys

Materials & Design (1980-2015) ◽

10.1016/j.matdes.2009.11.019 ◽

2010 ◽

Vol 31 (4) ◽

pp. 2134-2139 ◽

Cited By ~ 9

Author(s):

R.C. Dimitriu ◽

H.K.D.H. Bhadeshia

Keyword(s):

Growth Rate ◽

Fatigue Crack ◽

Crack Growth Rate ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Fatigue Crack Growth Rate ◽

Metallic Alloys ◽

Rate Model

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Fatigue Crack Growth Rate of Reeled Pipe in Sour Environments

Volume 4: Materials Technology ◽

10.1115/omae2015-41028 ◽

2015 ◽

Author(s):

Javad Safari ◽

Ramgopal Thodla ◽

Ian Merchant ◽

John Hamilton

Keyword(s):

Growth Rate ◽

Fatigue Crack ◽

Cyclic Loading ◽

Crack Growth Rate ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Fatigue Crack Growth Rate ◽

Paris Law ◽

Number Of Cycles ◽

Corrosive Environments

Fatigue Crack Growth Rate (FCGR) of reeled pipe (strained & aged) in sour environments was investigated. FCGR frequency scans on different microstructures, i.e. heat affected zone (HAZ), and weld center line (WCL), revealed that, FCGR in corrosive environments increased with decreasing frequency and reached a plateau value at low frequencies of 10mHz to 3mHz. At these ‘plateau frequencies’, FCGR in the moderately sour environment that was investigated were found to be about 10–18× or 30× higher than the in-air values for the WCL and HAZ, respectively. There was no effect of the reeling cycles on the FCGR of the WCL or HAZ specimens. The FCGRs of the WCL were consistently lower than that of the HAZ by about a factor of 2–3× under various conditions. The reason for the lower FCGR of the WCL is not well understood. It is possible that it may be due to the higher yield strength (YS) of the overmatched welds, differing hydrogen concentration and/or diffusion coefficient or possibly due to the differences in the microstructure between the HAZ and WCL. Paris law curves, FCGRs as a function of ΔK (stress intensity factor range), were measured on the HAZ, and WCL (both intrados) at the plateau frequency (10mHz), representative of flowline cyclic loading. They were also measured at a higher frequency of 0.33Hz, representative of Steel Catenary Risers (SCR) cyclic loading associated with wave motion. Comparisons of measured Paris law curves in corrosive environments to those in air were consistent with the results of the frequency scans. There was no effect of number of cycles of reeling on the Paris law curves in the sour environment tested for WCL and HAZ specimens at both the plateau frequency and 0.33Hz. The results of the test program suggest FCGR of WCL and HAZ in the sour environment tested are not affected by number of cycles (up to 5) of straining on the intrados side for the strain level (1.93% per cycle) used in this study.

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Evaluation of Crack Growth Behavior of Alloy 625 Under Cyclic Loading in a Steam Environment at 750°C

ASME 2011 Power Conference, Volume 2 ◽

10.1115/power2011-55471 ◽

2011 ◽

Author(s):

Yoichi Takeda ◽

Hirofumi Sato ◽

Shuhei Yamamoto ◽

Takamichi Tokunaga ◽

Akio Ohji

Keyword(s):

Growth Rate ◽

High Temperature ◽

Cyclic Loading ◽

Crack Growth Rate ◽

Crack Length ◽

Crack Growth ◽

Loading Rate ◽

Transition Period ◽

Growth Behavior ◽

Crack Growth Behavior

Advanced ultra supercritical (A-USC) steam power generation, in which high-pressure steam is raised to beyond 700°C, is being studied internationally. The creep strength of Ni-based super alloys evaluated at these high temperatures in an air environment makes these materials promising candidates for the material to be used for the structural components of these generators. Since they are exposed to high temperature steam, it is important that the effect of the environment on the degradation of these materials is investigated. In this investigation, the crack growth rate under cyclic loading in a 750°C steam environment using a compact tension specimen was evaluated. Crack length monitoring using the direct current potential drop technique was applied to the growing crack in a high temperature environment in order to evaluate the time-dependent behavior of the crack growth. The dependence of the loading rate and amplitude in terms of the stress intensity factor was obtained. The crack growth rate increased with decreasing loading rate and increasing amplitude. Multiple loading patterns were applied to a single specimen during crack length monitoring. When the loading pattern was changed to a different pattern, in most of the cases, the crack growth rate started to change and then became stable aftera transition period. The influence of intermetallics and different phases on the crack growth behavior is discussed based on the oxidation rate of these phases.

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