Fatigue Crack Growth Rate Behavior of A36 Steel using ASTM Load-Reduction and Compression Precracking Test Methods

Newman, J. C.; Ziegler, B.; Shaw, J. W.; Cordes, T. S.; Lingenfelser, D. J.

doi:10.1520/stp49542t

Cited by 3 publications

(4 citation statements)

References 17 publications

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“…A boundary element analysis was conducted using the FADD2D code for a shortened ESE(T) specimen (96.5 mm instead of 141 mm in this case). The purpose of the analysis was to derive the stress intensity factor ( K ) solution and back‐face strain relationships for the shortened version and compare them with the published solution for the full length ESE(T) specimen . From these analyses, the compliance based crack length relation and stress intensity factor results for the shortened version were within 1% or less of the full length version equations.…”

Section: Testingmentioning

confidence: 99%

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Improved test method and analytical modelling for fatigue crack growth in coarse‐grain titanium alloy with rough fatigue surfaces

Walker

Newman

2014

Fatigue Fract Eng Mat Struct

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Fatigue crack growth rate properties are typically determined by experimental methods in accordance with ASTM Standard E647. These traditional methods use standard notched specimens that are precracked under cyclic tensile loads before the main test. The data that are produced using this approach have been demonstrated elsewhere to be potentially adversely affected by the test method, particularly in the threshold region where load reduction (LR) methods are also required. Coarse‐grained materials that exhibit rough and tortuous fatigue surfaces have been observed to be strongly affected by the tensile precracking and LR, in part because the anomalies caused by crack closure and roughness‐induced closure become more important. The focus of the work reported in this paper was to further develop methods to determine more accurate fatigue crack growth rate properties from threshold through to fracture for coarse‐grained, β‐annealed, titanium alloy Ti‐6Al‐4V extra low interstitial thick plate material. A particular emphasis was put upon the threshold and near threshold region, which is of strong importance in the overall fatigue life of components. New approaches that differ from the ASTM Standard included compression precracking, LR starting from a lower load level and continuing the test beyond rates where crack growth would otherwise be considered below threshold. For the threshold regime, two LR methods were also investigated: the ASTM method and a method where the load is reduced with crack growth such that the crack mouth opening displacement is held constant, in an attempt to avoid remote closure. Constant amplitude fatigue crack growth rate data were produced from threshold to fracture for the titanium alloy at a variety of stress ratios. Spike overload tests were also conducted These data were then used to develop an improved analytical model to predict crack growth under spectrum loading and the predictions were found to correlate well with test results.

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Section: Testingmentioning

confidence: 99%

“…From these analyses, the compliance based crack length relation and stress intensity factor results for the shortened version were within 1% or less of the full length version equations. Thus, the existing equations for the full length specimen were considered acceptable.…”

Section: Testingmentioning

confidence: 99%

Improved test method and analytical modelling for fatigue crack growth in coarse‐grain titanium alloy with rough fatigue surfaces

Walker

Newman

2014

Fatigue Fract Eng Mat Struct

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“…The near-threshold regimes are shaded in yellow and correspond directly to the shaded regions in Figure 5 b. In the near-threshold regimes, CA cyclic loads were designed to keep the range of stress-intensity factors, ∆K, close to the near-threshold stress intensity factor of A36 structural steel, which was found to be approximately 3 MPa-m 1/2 [ 57 ]. In the near-threshold crack growth regimes, the fatigue crack did not grow notably (black line (thinner) in Figure 10 ), which is consistent with the 3D-DIC measurements (discussed regarding Figure 9 ).…”

Section: Resultsmentioning

confidence: 99%

Performance Evaluation of a Carbon Nanotube Sensor for Fatigue Crack Monitoring of Metal Structures

Ahmed

Schumacher

Thostenson

et al. 2020

Sensors

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This article describes research that investigated the ability of a carbon nanotube (CNT) sensor to detect and monitor fatigue crack initiation and propagation in metal structures. The sensor consists of a nonwoven carrier fabric with a thin film of CNT that is bonded to the surface of a structure using an epoxy adhesive. The carrier fabric enables the sensor to be easily applied over large areas with complex geometries. Furthermore, the distributed nature of the sensor improves the probability of detecting crack initiation and enables monitoring of crack propagation over time. Piezoresistivity of the sensor enables strains to be monitored in real time and the sensor, which is designed to fragment as fatigue cracks propagate, directly measures crack growth through permanent changes in resistance. The following laboratory tests were conducted to evaluate the performance of the sensor: (1) continuous crack propagation monitoring, (2) potential false positive evaluation under near-threshold crack propagation conditions, and (3) crack re-initiation detection at a crack-stop hole, which is a commonly used technique to arrest fatigue cracks. Real-time sensor measurements and post-mortem fractography show that a distinguishable resistance change of the sensor occurs due to fatigue crack propagation that can be quantitatively related to crack length. The sensor does not show false positive responses when the crack does not propagate, which is a drawback of many other fatigue sensors. The sensor is also shown to be remarkably sensitive to detecting crack re-initiation.

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“…The model agreed fairly well in the early stages of crack growth for 0.33 < c/w < 0.55, but over estimated the crack‐opening ratio by about 10% for 0.55 < c/w < 0.8. It has been observed that low R and high R fatigue crack growth rate data on a Δ K ‐rate basis are merging for deep cracks in bend‐type specimens, indicating a lack of crack closure (plane strain conditions). Solanki et al have found that under pure plane strain conditions on a bend‐type specimen under R = 0 loading, crack closure would not occur, but using the same model for a tension‐type specimen, crack closure was observed at a fairly high level.…”

Section: Fatigue Crack Growth Tests and Modellingmentioning

confidence: 99%

Fatigue crack growth in 7249‐T76511 aluminium alloy under constant‐amplitude and spectrum loading

Newman

Walker

Liu

2014

Fatigue Fract Eng Mat Struct

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Fatigue crack growth tests were conducted on compact, C(T), specimens made of 7249‐T76511 aluminium alloy. These tests were conducted to generate crack growth rate data from threshold to near fracture over a wide range of load ratios (R). Four methods were used to generate near threshold data: (1) ASTM E‐647 load reduction (LR), (2) compression pre‐cracking constant‐amplitude (CPCA), (3) compression pre‐cracking LR, and (4) constant crack mouth opening displacement LR method. A crack closure analysis was used to develop an effective stress‐intensity factor range against rate relation using a constraint factor (α = 1.85). Simulated aircraft wing spectrum tests were conducted on middle crack tension, M(T), specimens using a modified full‐scale fatigue test spectrum. The tests were used to develop the constraint‐loss regime (plane strain to plane stress; α = 1.85 to 1.15) behaviour. Comparisons were made between the spectrum tests and calculations made with the FASTRAN life prediction code; and the calculated crack growth lives were generally with ±10% of the test results.

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Fatigue Crack Growth Rate Behavior of A36 Steel using ASTM Load-Reduction and Compression Precracking Test Methods

Cited by 3 publications

References 17 publications

Improved test method and analytical modelling for fatigue crack growth in coarse‐grain titanium alloy with rough fatigue surfaces

Improved test method and analytical modelling for fatigue crack growth in coarse‐grain titanium alloy with rough fatigue surfaces

Performance Evaluation of a Carbon Nanotube Sensor for Fatigue Crack Monitoring of Metal Structures

Fatigue crack growth in 7249‐T76511 aluminium alloy under constant‐amplitude and spectrum loading

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