Three-Dimensional Crack Growth Assessment By Microtopographic Examination

Lloyd, W.R.; Piascik, Robert S.

doi:10.1520/stp16391s

Cited by 5 publications

(8 citation statements)

References 2 publications

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“…These studies of the same physical test specimens [2,3], performed independently by INEEL and University of South Carolina showed CTOA at small a were different in the interior than on the surface. CTOA assessed by both approaches -microtopography and surface imagingconverged toward similar values with increasing crack extension.…”

Section: -D Aspects Of Ctoa Assessmentmentioning

confidence: 88%

“…Investigations by Lloyd and Piascik [3] and Sutton et al [2] clearly show that CTOA can have strong dependence on through-thickness position, even in thin sheet materials. Their work also show substantial transient variation in CTOA immediately following crack initiation until the crack has advanced -at the specimen surface -the order of one sheet thickness in 7075 aluminum alloy.…”

Section: Experimental Measurement Methodsmentioning

confidence: 97%

“…There are various definitions of CTOA, usually based on the method of experimental measurement. These are detailed in Sutton et al [2], Lloyd and Piascik [3], Zerbst et al [7], and others. The most widely accepted definition measures the opening displacement between the crack flanks at a distance of 1 mm behind the instantaneous crack tip location.…”

Section: Ctoa Fundamentalsmentioning

confidence: 99%

“…INEEL, National Aeronautics and Space Administration (NASA), and University of South Carolina (USC) used various measurement techniques to determine the CTOA in 2.5 mm thick, 7075 aluminum M(T) specimens [2,3]. These specimens simulated cracks growing in aircraft skin material.…”

Section: -D Aspects Of Ctoa Assessmentmentioning

confidence: 99%

“…Investigations over the past ten years by different researchers, e.g. Dawicke et al [1], Sutton et al [2], and Lloyd and Piascik [3] show that the CTOA is a credible parameter that adequately characterizes the ductile fracture material response following crack initiation.…”

Section: Introductionmentioning

confidence: 99%

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Microtopography for ductile fracture process characterization Part 2: application for CTOA analysis

Lloyd

McClintock

2003

Engineering Fracture Mechanics

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The crack tip opening angle (CTOA) is seeing increased use to characterize fracture in so-called "low constraint" geometries, such as thin sheet aerospace structures and thin-walled pipes. With this increase in application comes a need to more fully understand and measure actual CTOA behavior. CTOA is a measure of the material response during ductile fracture, a "crack tip response function." In some range of crack extension following growth initiation, a constant value of CTOA is often assumed. However, many questions concerning the use of CTOA as a material response-characterizing parameter remain. For example, when is CTOA truly constant? What three-dimensional effects may be involved (even in thin sheet material)? What are the effects of crack tunneling on general CTOA behavior? How do laboratory specimen measurements of CTOA compare to actual structural behavior?Measurements of CTOA on the outer surface of test specimens reveal little about threedimensional effects in the specimen interior, and the actual measurements themselves are frequently difficult. The Idaho National Engineering and Environmental Laboratory (INEEL) use their microtopography system to collect data from the actual fracture surfaces following a test. Analyses of these data provide full three-dimensional CTOA distributions, at any amount of crack extension. The analysis is accomplished using only a single specimen and is performed entirely after the completion of a test. The resultant CTOA distributions allow development of full and effective understanding of CTOA behaviors. This paper presents underlying principles, various sources of measurement error and their corrections, and experimental and analytical verification of CTOA analysis with the microtopography method.

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Section: -D Aspects Of Ctoa Assessmentmentioning

confidence: 88%

Section: Experimental Measurement Methodsmentioning

confidence: 97%

Section: Ctoa Fundamentalsmentioning

confidence: 99%

Section: -D Aspects Of Ctoa Assessmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microtopography for ductile fracture process characterization Part 2: application for CTOA analysis

Lloyd

McClintock

2003

Engineering Fracture Mechanics

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Evaluation of fracture toughness of thin sheet of interstitial free high strength steel through critical crack tip opening angle (CTOA $$_\mathrm{c}$$ c ) measurement

2015

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Conventional testing of fracture toughness measurement for thin metallic sheets is not possible owing to the large plastic zone ahead of the crack tip. Hence, the critical-crack tip opening angle (CTOA c ) has been considered to be the key parameter to evaluate resistance of a thin sheet against stable crack propagation. In the present work, attempt has been made to measure the CTOA c of interstitial free high strength steel (IFHS) with 1 mm thickness using compact tension C(T) specimen. A high speed camera has been used for monitoring and imaging the progress of the crack length and crack tip angle during loading. The CTOA c measured from these photographs found to be 12 • ± 1.5 • . In these experiments, the crack tip velocity was also varied from 1.9 to 960 mm/min and no changes in the CTOA c value were observed. The high ductility of IFHS steel along with prevailing plane stress condition might be the reason of appreciably large CTOA c value.Keywords Fracture toughness · Crack tip opening angle (CTOA) · Interstitial free high strength (IFHS) steel · High speed imaging S. Koley (B) · S. Chatterjee · M. Shome Research and Development, Tata Steel, Jamshedpur,

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Three-Dimensional Analyses of Crack-Tip-Opening Angles and δ5-Resistance Curves for 2024-T351 Aluminum Alloy

James

Newman

Johnston

2002

Fatigue and Fracture Mechanics: 32nd Volume

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The objective of this paper was to investigate the fracture behavior of compact and middle-crack tension specimens made of 6.35 mm thick 2024-T351 aluminum alloy. Tests were conducted on compact tension, C(T), specimens ranging in width from 51 to 152 mm and on middle-crack tension, M(T), specimens ranging in width from 76 to 1016 mm. Most of the M(T) specimens were allowed to buckle during the fracture tests. Three-dimensional, elastic-plastic, finite-element analyses (FEA) using the WARP3D code with straight-front cracks were used to show transferability of the critical crack-tip-opening angle (CTOA) fracture criterion from small laboratory specimens, such as the C(T) specimen to large M(T) specimens. A single value of critical CTOA (Ψc = 6.35°) was determined from the FEA (with a straight-crack front) by matching the average failure load for the 152 mm C(T) specimens. CTOA analyses were then conducted on the various width C(T) and M(T) specimens. The WARP3D analyses with the critical CTOA predicted the experimental failure loads within ±3% for all specimens. The δ5-resistance curves from the analyses of the C(T) and M(T) specimens were nearly identical up to the maximum load. Beyond maximum load, the δ5-resistance curves for the C(T) specimens began to deviate rapidly; whereas, the δ5-resistance curves for the M(T) specimens only deviated slightly.

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Three-Dimensional Crack Growth Assessment By Microtopographic Examination

Cited by 5 publications

References 2 publications

Microtopography for ductile fracture process characterization Part 2: application for CTOA analysis

Microtopography for ductile fracture process characterization Part 2: application for CTOA analysis

Evaluation of fracture toughness of thin sheet of interstitial free high strength steel through critical crack tip opening angle (CTOA $$_\mathrm{c}$$ c ) measurement

Three-Dimensional Analyses of Crack-Tip-Opening Angles and δ5-Resistance Curves for 2024-T351 Aluminum Alloy

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