December 2005 

NASA/TM-2005-213948 

 

NASA Engineering and Safety Center 

Materials Super Problem Resolution Team 

Activity Report 

Fatigue Crack Growth Rate of Inconel 718 

Sheet at Cryogenic Temperatures 

Douglas Wells 

NASA Marshall Space Flight Center, Marshall Space Flight Center, Alabama 

Jonathan Wright and Keith Hastings 

Jacobs/Sverdrup 

NASA Marshall Space Flight Center, Marshall Space Flight Center, Alabama 
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December 2005 

NASA/TM-2005-213948 

 

NASA Engineering and Safety Center 

Materials Super Problem Resolution Team 

Activity Report 

Fatigue Crack Growth Rate of Inconel 718 

Sheet at Cryogenic Temperatures 

Douglas Wells 

NASA Marshall Space Flight Center, Marshall Space Flight Center, Alabama 

Jonathan Wright and Keith Hastings 

Jacobs/Sverdrup 

NASA Marshall Space Flight Center, Marshall Space Flight Center, Alabama 
Available from: 

NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS) 

7121 Standard Drive 5285 Port Royal Road 

Hanover, MD 21076-1320 Springfield, VA 22161-2171 

(301) 621-0390 (703) 605-6000 

ACKNOWLEDGMENTS 

Testing materials in extreme environments always requires a significant effort. Delicate tests, such as 

threshold fatigue crack growth rate, create an even greater challenge. The authors would like to thank the 

following individuals for their contributions to the overall effort to generate this data. 

From NASA LaRC, NESC, and affiliates: 

John Newman 

Bob Piascik 

From NASA MSFC: 

Bruce Bice 

James Hodo 

Ed Johnson 

Tina Malone 

Preston McGill 

From Jacobs-Sverdrup and affiliates at NASA MSFC: 

Robert Bond 

Jeff Clounch 

Harold Ellett 

Matt Gargis 

Ricky Goodwin 

Keith Hastings 

Matt Jackson 

Bill Malone 

Randy Millwood 

David Motes 

Lisa Sharff 

Craig Stafford 

Myron Tapscott 

Mike Watwood 

The use of trademarks or names of manufacturers in the report is for accurate reporting and does not 

constitute an official endorsement, either expressed or implied, of such products or manufacturers by the 

National Aeronautics and Space Administration.
1 of 18 

Table of Contents 

Abstract.......................................................................................................................................... 2 

NESC Executive Summary .......................................................................................................... 2 

Introduction................................................................................................................................... 2 

Materials ........................................................................................................................................ 3 

Experimental Procedures............................................................................................................. 3 

Test Results and Discussion ......................................................................................................... 4 

Conclusions.................................................................................................................................... 6 

References...................................................................................................................................... 7 
2 of 18 

Abstract 

Inconel 718 sheet material was tested to determine fatigue crack growth 

rate (FCGR) at cryogenic conditions representative of a liquid hydrogen 

(LH2) environment at -423o

F. Tests utilized M(T) and ESE(T) specimen 

geometries and environments were either cold gaseous helium or 

submersion in LH2. The test results support a significant improvement in 

the fatigue crack growth threshold at -423oF compared to -320oF or 70oF. 

NESC Executive Summary 

This report summarizes material characterization tests performed under the auspices of the 

Materials Super Problem Resolution Team (SPRT) to provide confirmation and closure for LH2

FCGR properties utilized in the NASA Engineering and Safety Center (NESC) Independent 

Technical Assessment (ITA) of the Orbiter Flowliner system [ref. 5]. For comparison and 

completeness, prior tests run for the Space Shuttle Integration Office in gasified LHe are also 

included. 

Introduction 

A typical articulated joint in a cryogenic fuel or oxidizer supply line requires either an external 

gimbal support or an internal central support mechanism, and a formed, pressure carrying 

bellows to allow for motion. To keep the flow field in the line from interacting with the bellows, 

a liner is placed over the bellows to make the internal dimensions of the feedline smooth by 

hiding the bellows from the flow field. See Figures 1a and 1b. The lines within the Orbiter that 

carry LH2 and liquid oxygen (LO2) from the External Tank to the Space Shuttle Main Engines 

are fabricated of thin sheet Inconel 718 material and contain similar “flow-liners” at the 

articulated joints. In this case, slots were placed into the flow-liners to allow pressure 

communication between the main flow channel and the space between the liner and bellows. An 

example of flow-liners and their slots are shown in Figure 2. In the spring of 2002, a small 

number of cracks were identified growing from the slots on the flow-liners in the hydrogen 

supply lines on many of the Orbiters. An example of a transverse crack is shown in Figure 3. 

The FCGR data at LH2 temperature is important to the damage tolerance assessment of the flowliner structure, particularly when the test data supports a slower crack growth rate than is 

represented by existing data at -320o

F or 70oF. To begin, FCGR data was generated at -423oF 

using a gasified LHe environment. This effort was funded directly by the Space Shuttle 

Integration Office to support ongoing flow-liner assessments at that time. During the NESC ITA 

of the Orbiter flow-liner system, the suitability of the gasified LHe test environment was 

questioned. Due to the potential for deleterious effects of hydrogen on Inconel 718 under some 

conditions (typically high pressure gaseous hydrogen at room temperature) and the potential 

influence of the liquid environment on FCGR, the Materials SPRT chose to support confirmation 

tests directly in LH2. All of the tests at -423o

F reported herein are complementary to the results 
3 of 18 

published [ref. 1] for Inconel 718 base metal and welds at room and cryogenic temperatures 

down to -320o

F. 

Materials 

The materials used for the tests were processed to match the condition of the Orbiter flow-liner 

hardware as closely as possible. Thin sheet (0.050 inches) was ordered from SAE AMS 5596 

[ref. 2], which supplies material in the solution heat-treated condition at 1,775oF. The 

documentation pertaining to the fabrication of the flow-liner hardware dictates an aging cycle 

that is non-standard for Inconel 718: 3 hours at 1,400oF. To match the hardware, the materials 

for these tests were aged in a vacuum environment for 3 hours +/- 10 minutes at 1,400oF +/- 25oF. 

The influence of this non-standard aging practice is discussed below with comparisons to 

existing data with more traditional heat-treated conditions. Materials [ref. 1] were also heattreated to these conditions. Limited tensile testing of this material in LH2 produced an average 

yield strength of 185 ksi and an average ultimate strength of 265 ksi. 

Experimental Procedures 

Test Procedures 

All test procedures were in accordance with ASTM E 647, Standard Test Method for 

Measurement of Fatigue Crack Growth Rates [ref. 3]. All tests used digitally-controlled servohydraulic machines which were controlled directly by an ADwin Gold system from Fracture 

Technology Associates. Test techniques included constant load amplitude, constant load ratio 

with a controlled K-gradient and the Kmax load shedding technique with an increasing load ratio. 

Crack lengths were measured continuously using compliance techniques with a front-face clip 

gage. Following test completion, the pre-crack and final crack lengths were measured optically. 

Small corrections were made to the compliance crack length data as needed based on the optical 

measurements. 

Test Samples 

Two test sample designs were used in this test series: the Eccentrically-loaded Single Edge 

crack Tension sample (ESE(T)) with a width of 1.5 inches and the Middle Crack Tension sample 

(M(T)) with a width of 2.0 inches. Figure 4 shows an example of both sample designs following 

testing. All test samples were pre-cracked in air at acceptable stress intensities to avoid load 

history interaction with the crack growth rates during the test. For all tests, the fracture samples 

were oriented in the T-L direction relative to the rolling direction of the material. 

Environments 

Test techniques were generally verified in room temperature air and liquid nitrogen (LN2) 

environments prior to attempting the -423o

F environment with LHe or LH2. The LHe tests were 

run using a continuous supply of LHe into a well insulated test chamber supported between the 

uprights of the test machine allowing the sample to move independently from the chamber. A 
4 of 18 

system of small tubes with orifices distributed the LHe evenly within the box. The LHe is in a 

gaseous state by the time it is expelled from the tubes. See Figure 5. Therefore, a more accurate 

description of the test chamber environment is cold gaseous helium. To supply LHe 

continuously for the time required for these tests, a 5,000 gallon tanker truck was used. The 

ullage pressure in the tanker was maintained using a high purity gaseous helium supply trailer. 

The flow rate of LHe into the test rig was controlled with regulators, but the ullage pressure of 

the tanker had a strong influence on the actual flow rates realized. Therefore, the test rig 

required continuous monitoring. The test environment in the LHe rig was maintained at -423o

F 

+5o

F/-10oF throughout the test operation. Thermocouples attached to both sides of the test 

sample and floating free in the chamber were continuously monitored. 

The LH2 environment was obtained in the NASA MSFC Hydrogen Test Facility (HTF). 

Specially designed for testing directly in various hydrogen environments, the HTF provides a 

unique ability to overcome the hazards of hydrogen testing and permits direct submersion of the 

test sample in LH2 throughout the test. Figures 6a and 6b show the LH2 cryogenic test rig. 

Proper test temperature is assured by maintaining complete submersion in LH2 by means of an 

automated system for filling the cryostat. The sample temperature is known to be -423oF after a 

moderate soak period. 

Test Results and Discussion 

A summary table of the tests reported is included in Table 1. 

Table 1. Summary of Test Samples and Conditions 

Test ID Sample Type Environment Load Ratio Method 

LHe-ESET-1 ESE(T) Gasified LHe (-423oF) Increasing Kmax = 30 

LHe-ESET-2 ESE(T) Gasified LHe (-423oF) Increasing Kmax = 30 

LHe-ESET-3 ESE(T) Gasified LHe (-423oF) Increasing Kmax = 50 

LHe-ESET-5 ESE(T) Gasified LHe (-423oF) R = 0.1 Incr. K-grad. 

LHe-ESET-6 ESE(T) Gasified LHe (-423oF) R = 0.1 Incr. K-grad. 

LN2-ESET-1 ESE(T) LN2 (-320oF) Increasing Kmax = 30 

RT-ESET-1 ESE(T) Lab Air (70oF) Increasing Kmax = 30 

RT-ESET-2 ESE(T) Lab Air (70oF) Increasing Kmax = 30 

LH2-MT-1 M(T) LH2 (-423oF) R = 0.8 Const. load 

LH2-MT-2 M(T) LH2 (-423oF) R = 0.8 Const. load 

LH2-MT-3 M(T) LH2 (-423oF) R = 0.8 Const. load 

LH2-MT-4 M(T) LH2 (-423oF) R = 0.8 Const. load 

LH2-MT-5 M(T) LH2 (-423oF) R = 0.8 Const. load 

LH2-MT-6 M(T) LH2 (-423oF) R = 0.2 Const. load 

LH2-ESET-B ESE(T) LH2 (-423oF) Increasing Kmax = 30 

LH2-ESET-C ESE(T) LH2 (-423oF) Increasing Kmax = 30 
5 of 18 

Preliminary Tests 

Prior to performing testing at -423o

F in LHe or LH2, Kmax tests were run using the ESE(T) 

sample in air at room temperature and in LN2. A favorable comparison to the test data generated 

by Newman [ref. 1], and to available data in NASGRO®, confirmed the basic test techniques to 

be used for the colder tests. An example of this comparison is shown in Figure 7, where data by 

Garr [ref. 4] is plotted at three R-ratios against Kmax data [ref. 1] from the current study. At high 

R-ratio (0.7 to 0.9), all data sources are in general agreement. The material heat treatment 

condition for the material [ref. 4] is as follows: solution heat treat at 1,900o

F followed by a twostep aging at 1,400o

F for 10 hours and 1,200oF for 10 hours. This is a more common heat treat 

condition for Inconel 718 used at cryogenic temperatures. Inconel 718 is a complicated alloy 

relying on precipitation during aging for its properties. No effort was made during any of the 

flow-liner investigations to determine the effect of the non-standard aging practice on the 

development of the microstructure. Differences between the flow-liner aging and standard aging 

practice likely reveals itself in the microstructure, but it is not known how this may affect the 

mechanical behavior of the alloy. The agreement shown in Figure 7 for FCGR in LN2 is the best 

available justification for the use of this data in other applications beyond the flow-liner 

assessment, which have a more traditional heat treatment. 

Tests in Gasified LHe 

Note in Figure 7 that the approximate high R-ratio threshold for these tests in LN2 is about 3.5 

ksi√in. The motivation for testing in an atmosphere representative of the LH2 within the 

hydrogen feedline was to either support the use of the LN2 data or improve on the data if possible, 

where improvement is considered a reduction in crack growth rate for a given ΔK. Figure 8 

presents the results of five tests in the LHe rig, each using the ESE(T) sample. Three tests were 

run using the Kmax methodology with Kmax = 30 ksi√in for two tests and Kmax = 50 ksi√in for the 

third test. Each test was run with a K-gradient of -20 in-1. Two tests were run at constant load 

ratio, R = 0.1, with an increasing K-gradient. All tests were conducted at 20 Hz. The Kmax tests 

are very consistent and are ordered appropriately with their final R-ratio values: at threshold, 

right to left in Figure 8, the R-ratio values are 0.72, 0.74 and 0.86. This data in LHe supports a 

considerable improvement in the crack growth rates over the available data in LN2, particularly 

as the crack growth rates approach threshold. Steady state, region II, growth rates modestly 

improve as well. 

Tests in LH2

The confirmation tests performed in LH2 were designed to take a different approach to confirm 

the results shown in LHe. Taking the extra effort to test directly in LH2 provides an answer to 

many questions which naturally arise when representing the flow-liner environment solely by 

temperature alone in the LHe rig. The LH2 tests are much closer to the actual use environment 

and allow any influence of the presence of hydrogen as well as the liquid itself to be included in 

the test. The only aspect of the flow-liner environment not included is the high frequency 

(>1000 Hz) of the cyclic loading in the hardware. All tests in LH2 were conducted at 20 Hz. To 

provide an additional means of confirmation of the LHe results, the test sample design was 

changed to the M(T) sample and the loading conditions were set to keep the R-ratio constant 

with a constant load amplitude throughout the test. Thus, the crack growth alone creates the 

increasing K-gradient and it is not constant. Besides simplicity, an advantage this test procedure 
6 of 18 

provides is an easy test history to model using crack growth analytical tools such as NASGRO®

to verify the material constants derived from the data and used in the analysis. The results of six 

M(T) tests are shown in Figure 9a. The tests were designed to start at progressively lower initial 

ΔK values with the intent of eventually having the crack growing just above threshold. Test 

LH2-MT-5 came closest, but was not considered a substantial confirmation of the LHe threshold 

value. The expense of LH2 testing prevented another attempt at a lower initial ΔK value. Figure 

9b shows the same constant-R M(T) data with the addition of the ESE(T) constant-R LHe data at 

R = 0.1. The data is consistent between the two test methods, noting that the R = 0.2 LH2 data 

falls parallel and just above the LHe R = 0.1 data. 

To improve the chances of getting data in the LH2 environment that would confirm LHe 

threshold values, two tests were run using the same test technique employed in LHe: ESE(T) 

samples tested with the Kmax methodology. Figure 10 shows the results of these two tests 

compared against the LHe Kmax tests. In both cases, the LH2 tests continued to shed until the ΔK 

reached approximately 10-11 ksi√in. At this point, the crack growth rates dropped substantially 

and did not follow the gentle curve to threshold shown by the LHe tests, which dropped to 

approximately 7-8 ksi√in. The cause of this change in behavior is not known. The early 

portions of the LH2 tests are in good agreement with the LHe data and no test difficulties arose 

that would invalidate the tests. However, the early drop in crack growth rate compared to the 

LHe tests can not be construed as a higher threshold value. 

Conclusions 

Though none of the tests run in LH2 recorded data within the ASTM-defined threshold regime, 

the agreement of the results between LHe and LH2 on all accounts is good. The tests in LH2 did 

confirm that no unforeseen effects of the LH2 environment influenced the results generated in 

LHe. The primary product of this test series is the change in FCGR threshold for Inconel 718 

with decreasing temperature. Figure 11 shows a summary of test results taken from this study 

and [ref. 1]. Results are grouped by temperature and are shown at 70o

F, -320oF and -423oF. The 

increase in threshold is clearly evident and is supported by all test data. The high R-ratio 

threshold at -423oF, 7 ksi√in is approximately twice that at -320oF, 3.5 ksi√in. The FCGR values 

for Inconel 718 in LH2 used in the flow-liner assessment [ref. 5] are fully supported by tests in 

LHe and LH2. For reference only, a revised curve-fit for an average representation of the data in 

NASGRO® (version 4.x) is provided in Figure 12. 

 
7 of 18 

References 

1. Newman, John A., Smith, Stephen W., Willard, Scott A., Piascik, Robert S., “A 

Comparison of Weld-Repaired and Base Metal for Inconel 718 and CRES 321 at 

Cryogenic and Room Temperatures”, NASA/TM-2004-213253, August 2004. 

2. “Nickel Alloy, Corrosion and Heat Resistant, Sheet, Strip, Foil and Plate; 52.5NI-19Cr3.0Mo-5.1Cb-0.90Ti-0.50Al-18Fe; Consumable Electrode or Vacuum Induction Melted, 

1775F (968C) Solution Heat Treated”, Society of Automotive Engineers Aerospace 

Material Specification, SAE AMS 5596, SAE International, 400 Commonwealth Drive, 

Warrendale, PA 15096-0001. 

3. “Standard Test Method for Measurement of Fatigue Crack Growth Rates”, Annual Book 

of ASTM Standards, Vol. 3.01, E 647, American Society for Testing and Materials, West 

Conshohocken, PA, 2001. 

4. NASGRO® Fracture Mechanics and Fatigue Crack Growth Rate Software. Developed 

and distributed under the terms of a Space Act Agreement between NASA Johnson Space 

Center and Southwest Research Institute (www.nasgro.swri.org). Material data 

referenced under code Q3LC10LA4: Garr, K. R., Fatigue Crack Growth Rate and JIntegral Fracture Toughness of Inconel 718”, Rockwell International – Rocketdyne 

Division. Data received from Ken Garr on June 24, 1988. 

5. “Orbiter LH2 Feedline Flowliner Cracking Problem Independent Technical Assessment 

(ITA) Report”, NASA Engineering and Safety Center Report, RP-04-11/04-004-E, 

Version 1.0, July 20, 2004, NASA/TM-2005-213787. 
8 of 18 

Figure 1a, b. Typical configuration of flow-liner components. Pressure Carrier Bellows 

provides containment and flexibility in the feed-line while flow-liner hides the bellows 

from the flow field. 

FLOW

FLOW

(a)

(b)

Figure 1a, b. Typical configuration of flow-liner components. Pressure Carrier Bellows 

provides containment and flexibility in the feed-line while flow-liner hides the bellows 

from the flow field. 

FLOW

FLOW

(a)

(b)
9 of 18 

Figure 2. Inconel 718 flow-liners 

shown during inspection. Cracks in 

the flow-liners in the liquid 

hydrogen supply lines were only 

found at the gimbal joint location 

directly adjacent to the Main Engine 

Low Pressure Fuel Pump Flange, 

shown.

Figure 3. An example 

of a crack identified in 

the flow-liner. In this 

case, a transverse crack 

likely influenced by the 

proximity of a repair 

weld.

Figure 2. Inconel 718 flow-liners 

shown during inspection. Cracks in 

the flow-liners in the liquid 

hydrogen supply lines were only 

found at the gimbal joint location 

directly adjacent to the Main Engine 

Low Pressure Fuel Pump Flange, 

shown.

Figure 3. An example 

of a crack identified in 

the flow-liner. In this 

case, a transverse crack 

likely influenced by the 

proximity of a repair 

weld.
10 of 18 

Figure 4. Test samples in use in the current study. Middle Crack Tension, M(T) (top) and the Eccentrically 

Loaded Single-Edge Crack Tension, ESE(T).
11 of 18 

Figure 5. Temporary cryostat 

fabricated to perform gasified liquid 

helium tests. Note the interlaced 

copper spray-bar arrangement which 

provided even cooling of the chamber 

and a more gentle introduction of the 

cold helium gas. Liquid helium is 

pumped into the box, but it gasifies 

before exiting the spray-bar system.

Figure 6a,b. Liquid hydrogen test rig shown in open (a) and closed (b) configurations. The 

servo-hydraulic machine has its actuator at the top cross-member. The load reaction 

structure is attached to the top cross-member as well. The cryostat is brought up from 

below to submerge the sample and load reaction in LH2 throughout the test.

(a) (b)

Figure 5. Temporary cryostat 

fabricated to perform gasified liquid 

helium tests. Note the interlaced 

copper spray-bar arrangement which 

provided even cooling of the chamber 

and a more gentle introduction of the 

cold helium gas. Liquid helium is 

pumped into the box, but it gasifies 

before exiting the spray-bar system.

Figure 6a,b. Liquid hydrogen test rig shown in open (a) and closed (b) configurations. The 

servo-hydraulic machine has its actuator at the top cross-member. The load reaction 

structure is attached to the top cross-member as well. The cryostat is brought up from 

below to submerge the sample and load reaction in LH2 throughout the test.

(a) (b)
12 of 18 

Figure 7. Comparison of liquid nitrogen (-320F) test results for Inconel 718 from the 

NASGRO database and the present study

1 2 3 4 5 6 7 8 910 20 40 60 80 100 200

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

NASGRO 4.x (Q3LC10LA4) R = 0.1, -320F [4]

NASGRO 4.x (Q3LC10LA4) R = 0.7, -320F [4]

NASGRO 4.x (Q3LC10LA4) R = 0.9, -320F [4]

LN2-ESET-1 Kmax = 30

LN2-ESET-LaRC Kmax = 30 [1]

LN2-ESET-LaRC Kmax = 30 [1]

Figure 7. Comparison of liquid nitrogen (-320F) test results for Inconel 718 from the 

NASGRO database and the present study

1 2 3 4 5 6 7 8 910 20 40 60 80 100 200

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

NASGRO 4.x (Q3LC10LA4) R = 0.1, -320F [4]

NASGRO 4.x (Q3LC10LA4) R = 0.7, -320F [4]

NASGRO 4.x (Q3LC10LA4) R = 0.9, -320F [4]

LN2-ESET-1 Kmax = 30

LN2-ESET-LaRC Kmax = 30 [1]

LN2-ESET-LaRC Kmax = 30 [1]
13 of 18 

5 6 7 8 9 10 20 40 60 80 100 200

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

LHe-ESET-1 Kmax = 30

LHe-ESET-2 Kmax = 30

LHe-ESET-3 Kmax = 50

LHe-ESET-5 R = 0.1

LHe-ESET-6 R = 0.1

Figure 8. Test results for Inconel 718 in gasified liquid helium at -423F.

5 6 7 8 9 10 20 40 60 80 100 200

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

LHe-ESET-1 Kmax = 30

LHe-ESET-2 Kmax = 30

LHe-ESET-3 Kmax = 50

LHe-ESET-5 R = 0.1

LHe-ESET-6 R = 0.1

Figure 8. Test results for Inconel 718 in gasified liquid helium at -423F.
14 of 18 

5 6 7 8 9 10 20 40 60 80 100 200

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

LH2-MT-1 @ R = 0.8

LH2-MT-2 @ R = 0.8

LH2-MT-3 @ R = 0.8

LH2-MT-4 @ R = 0.8

LH2-MT-5 @ R = 0.8

LH2-MT-6 @ R = 0.2

Figure 9a. Test results for Inconel 718 in liquid hydrogen (-423F) using M(T) samples 

and a constant load ratio and amplitude.

5 6 7 8 9 10 20 40 60 80 100 200

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

LH2-MT-1 @ R = 0.8

LH2-MT-2 @ R = 0.8

LH2-MT-3 @ R = 0.8

LH2-MT-4 @ R = 0.8

LH2-MT-5 @ R = 0.8

LH2-MT-6 @ R = 0.2

Figure 9a. Test results for Inconel 718 in liquid hydrogen (-423F) using M(T) samples 

and a constant load ratio and amplitude.
15 of 18 

5 6 7 8 9 10 20 40 60 80 100 200

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

LHe-ESET-5 @ R = 0.1

LHe-ESET-6 @ R=0.1

LH2-MT-1 @ R = 0.8

LH2-MT-2 @ R = 0.8

LH2-MT-3 @ R = 0.8

LH2-MT-4 @ R = 0.8

LH2-MT-5 @ R = 0.8

LH2-MT-6 @ R = 0.2

Figure 9b. Constant load ratio tests in LHe (-423F) for Inconel 718 show 

consistency with results in LH2

5 6 7 8 9 10 20 40 60 80 100 200

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

LHe-ESET-5 @ R = 0.1

LHe-ESET-6 @ R=0.1

LH2-MT-1 @ R = 0.8

LH2-MT-2 @ R = 0.8

LH2-MT-3 @ R = 0.8

LH2-MT-4 @ R = 0.8

LH2-MT-5 @ R = 0.8

LH2-MT-6 @ R = 0.2

Figure 9b. Constant load ratio tests in LHe (-423F) for Inconel 718 show 

consistency with results in LH2
16 of 18 

5 6 7 8 9 10 20 40 60 80 100

10-9

10-8

10-7

10-6

10-5

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

LH2-ESET-B Kmax = 30

LH2-ESET-C Kmax = 30

LHe-ESET-1 Kmax = 30

LHe-ESET-2 Kmax = 30

LHe-ESET-3 Kmax = 50

Figure 10. Comparison of ESE(T) Kmax tests for Inconel 718 at -423F in 

LHe and LH2

5 6 7 8 9 10 20 40 60 80 100

10-9

10-8

10-7

10-6

10-5

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

LH2-ESET-B Kmax = 30

LH2-ESET-C Kmax = 30

LHe-ESET-1 Kmax = 30

LHe-ESET-2 Kmax = 30

LHe-ESET-3 Kmax = 50

Figure 10. Comparison of ESE(T) Kmax tests for Inconel 718 at -423F in 

LHe and LH2
17 of 18 

1 2 3 4 5 6 8 10 20 40 60 80 100

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

RT-ESET-1 Kmax = 30

RT-ESET-2 Kmax = 30

LN2-ESET-1 Kmax = 30

LN2-ESET-LaRC Kmax = 30 [1]

LHe-ESET-1 Kmax = 30

LHe-ESET-2 Kmax = 30

LHe-ESET-3 Kmax = 50

LH2-ESET-B Kmax = 30

LH2-ESET-C Kmax = 30

Figure 11. Test data supporting increasing high R-ratio threshold with 

decreasing temperature for Inconel 718 at 70F, -320F and -423F.

1 2 3 4 5 6 8 10 20 40 60 80 100

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

RT-ESET-1 Kmax = 30

RT-ESET-2 Kmax = 30

LN2-ESET-1 Kmax = 30

LN2-ESET-LaRC Kmax = 30 [1]

LHe-ESET-1 Kmax = 30

LHe-ESET-2 Kmax = 30

LHe-ESET-3 Kmax = 50

LH2-ESET-B Kmax = 30

LH2-ESET-C Kmax = 30

Figure 11. Test data supporting increasing high R-ratio threshold with 

decreasing temperature for Inconel 718 at 70F, -320F and -423F.
18 of 18 

5 6 7 8 910 20 40 60 80 100 200

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

C = 2.9e-010

n = 2.8

p = 0.25

q = 0.25

KIc = 100

Kc(@t) = 140

Kcmax = 140

KIe = 125

Ak = 0.75

Bk = 0.4

YS = 185

ΔK1

 = 7.0

α = 2

Cth(+) = 0

Cth(-) = 0

t = 0.05

Rcl = 0.7

SR = 0.3

Curve Fit R = 0.1

Curve Fit R = 0.8

Curve Fit R = 0.9

LHe-ESET-3 Kmax = 50

LHe-ESET-2 Kmax = 30

LHe-ESET-5 R = 0.1

LHe-ESET-6 R = 0.1

LH2-MT-1 R = 0.8

LH2-MT-3 R = 0.8

LH2-MT-5 R = 0.8

Figure 12. Potential NASGRO 4.x curve fit parameters shown for an 

average fit to Inconel 718 at -423F.

5 6 7 8 910 20 40 60 80 100 200

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Δ K (Ksi*(in)1/2)

da/dN (in / cycle)

C = 2.9e-010

n = 2.8

p = 0.25

q = 0.25

KIc = 100

Kc(@t) = 140

Kcmax = 140

KIe = 125

Ak = 0.75

Bk = 0.4

YS = 185

ΔK1

 = 7.0

α = 2

Cth(+) = 0

Cth(-) = 0

t = 0.05

Rcl = 0.7

SR = 0.3

Curve Fit R = 0.1

Curve Fit R = 0.8

Curve Fit R = 0.9

LHe-ESET-3 Kmax = 50

LHe-ESET-2 Kmax = 30

LHe-ESET-5 R = 0.1

LHe-ESET-6 R = 0.1

LH2-MT-1 R = 0.8

LH2-MT-3 R = 0.8

LH2-MT-5 R = 0.8

Figure 12. Potential NASGRO 4.x curve fit parameters shown for an 

average fit to Inconel 718 at -423F.
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Fatigue Crack Growth Rate of Inconel 718 Sheet at Cryogenic

Temperatures

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Wells, Douglas; Wright, Jonathan; and Hastings, Keith

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Engineering and Safety Center

Langley Research Center

Hampton, VA 23681-2199

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

 8. PERFORMING ORGANIZATION

 REPORT NUMBER

L-19198

10. SPONSOR/MONITOR'S ACRONYM(S)

NASA

13. SUPPLEMENTARY NOTES

NESC Materials Super Problem Resolution Team Activity Report

Wells: NASA Marshall Space Flight Center; Wright and Hastings: Jacobs/Sverdrup, NASA Marshall Space Flight Center

An electronic version can be found at http://ntrs.nasa.gov

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Unclassified - Unlimited

Subject Category 39

Availability: NASA CASI (301) 621-0390

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

Inconel 718 sheet material was tested to determine fatigue crack growth rate (FCGR) at cryogenic conditions representative of

a liquid hydrogen (LH2) environment at -423 degree F. Tests utilized M(T) and ESE(T) specimen geometries and

environments were either cold gaseous helium or submersion in LH2. The test results support a significant improvement in

the fatigue crack growth threshold at -423 degree F compared to -320 degree F or 70 degree F.

15. SUBJECT TERMS

NESC; Inconel 718; Liquid hydrogen; Liquid oxygen; Orbiter; Flow-liner; Test procedures

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(301) 621-0390

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5f. WORK UNIT NUMBER

104-08-31

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 NUMBER(S)

NASA/TM-2005-213948

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01- 12 - 2005