Study of Testing Method for Dynamic Initiation Toughness of Sandstone under Blasting Loading

In this paper, an internal central single-cracked disk (ICSCD) specimen was proposed for the study of dynamic fracture initiation toughness of sandstone under blasting loading. The ICSCD specimen had a diameter of 400 mm sandstone disc with a 60 mm long crack. Blasting tests were conducted by using the ICSCD specimens. The blasting strain-time curve was obtained from the radial strain gauges placed around the blast hole. The fracture initiation time was determined by circumferential strain gauges placed around the crack tip. The stress history on the blast hole of the sandstone specimen was then derived from measured strain curve through the Laplace transform. The numerical solutions were further obtained by the numerical inversion method. A numerical model was established using the finite element software ANSYS. The type I dynamic stress intensity factor curves of sandstone under blasting loading were derived by the mutual interaction integration method. The results showed that (1) the ICSCD specimen can be used to measure dynamic initiation fracture toughness of rocks; (2) the stress on the blast hole wall can be obtained by the Laplace numerical inversion method; (3) the dynamic initiation fracture toughness of the ICSCD sandstone specimen can be calculated by the experimental-numerical method with a maximum error of only 7%.

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The fracture toughness of martensite islands in dual-phase DP800 steel

Journal of Materials Research ◽

10.1557/s43578-021-00150-4 ◽

2021 ◽

Author(s):

Chunhua Tian ◽

Christoph Kirchlechner

Keyword(s):

Fracture Toughness ◽

Fracture Initiation ◽

Initiation Toughness ◽

Dual Phase ◽

Dp Steel ◽

Bending Tests ◽

Damage Initiation ◽

Linear Elastic ◽

Steel Grades

Abstract In situ microcantilever bending tests were performed on martensite islands in a dual-phase (DP) steel to extract the fracture toughness of martensite at the microscale and to understand damage initiation during forming of DP steels. All microcantilevers were produced through FIB milling. The martensite islands do not exhibit linear elastic brittle fracture; instead, significant ductile tearing is observed. The conditional fracture initiation toughness extracted by definition and by Pippan’s transfer criterion is Ki = 6.5 ± 0.4 MPa m1/2 and Ki,2% = 10.1 ± 0.3 MPa m1/2, respectively. The obtained value is well-represented by the strength-toughness trend of other ferritic steel grades. Considering the yield stress of the same martensite island, we found that crack initiation can occur only in very large martensite islands or in a banded or agglomerated martensite structure. Graphic abstract

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Testing Techniques for Establishing Fracture Resistance of Steel in a Sour Environment

Volume 4: Materials Technology ◽

10.1115/omae2017-62695 ◽

2017 ◽

Author(s):

Muhammad S. Ali

Keyword(s):

Fracture Toughness ◽

Fracture Resistance ◽

Crack Extension ◽

Pipeline Steel ◽

Fracture Initiation ◽

Load Level ◽

Manganese Steel ◽

Initiation Toughness ◽

Loading Rates ◽

Rate Of Increase

It is well established that sour operating environments can give rise to significantly reduced fracture toughness of pipelines made of carbon manganese steel. Fracture resistance of a material is usually defined in terms of a fracture resistance curve, commonly known as an R-curve which is determined by testing pre-cracked specimens under a rising load. Fracture resistance data can be derived by the single specimen method, where crack extension is determined using unloading compliance or the multiple specimen method, where crack extension is measured from the fracture face of each specimen and each specimen is taken to a different load level. The fracture resistance behaviour of API 5L X65 grade pipeline steel determined by testing single edge notched bend specimens in a specific sour environment using both single and multiple specimen test methods is reported. The fracture resistance of the steel was found to be highly sensitive to the loading rates (described by the initial rate of increase of stress intensity factor in the elastic range) applied during the fracture resistance tests. It was possible to identify a loading rate slow enough to provide fracture initiation toughness reasonably close to the expected lower bound toughness. It is possible to produce similar R-curves from single and multiple specimen testing methods (if conditions are otherwise the same). Under comparable loading rates and environmental conditions, side grooved specimens resulted in lower fracture toughness as compared to the toughness determined from the plane sided specimens. It was also noticed that there was a weaker correlation between side grooving and toughness at slower loading rates.

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Stretch-zone analysis by image processing for the evaluation of initiation fracture toughness of a HSLA steel

Zeitschrift für Metallkunde ◽

10.3139/146.101121 ◽

2005 ◽

Vol 96 (8) ◽

pp. 924-932

Author(s):

M. Tarafder ◽

Swati Dey ◽

S. Sivaprasad ◽

S. Tarafder ◽

M. Nasipuri

Keyword(s):

Image Processing ◽

Fracture Toughness ◽

Hsla Steel ◽

Stretch Zone ◽

Initiation Fracture Toughness

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Fracture Toughness Testing and its Implications to Engineering Fracture Mechanics Analysis of Energy Pipelines

Volume 1: Pipeline and Facilities Integrity ◽

10.1115/ipc2018-78723 ◽

2018 ◽

Author(s):

Sergio Limon ◽

Peter Martin ◽

Mike Barnum ◽

Robert Pilarczyk

Keyword(s):

Fracture Toughness ◽

Fracture Mechanics ◽

Test Data ◽

Fracture Mode ◽

Fracture Process ◽

Fracture Behavior ◽

Fracture Initiation ◽

Fracture Toughness Testing ◽

Final Fracture ◽

Toughness Testing

The fracture process of energy pipelines can be described in terms of fracture initiation, stable fracture propagation and final fracture or fracture arrest. Each of these stages, and the final fracture mode (leak or rupture), are directly impacted by the tendency towards brittle or ductile behavior that line pipe steels have the capacity to exhibit. Vintage and modern low carbon steels, such as those used to manufacture energy pipelines, exhibit a temperature-dependent transition from ductile-to-brittle behavior that affects the fracture behavior. There are numerous definitions of fracture toughness in common usage, depending on the stage of the fracture process and the behavior or fracture mode being evaluated. The most commonly used definitions in engineering fracture analysis of pipelines with cracks or long-seam weld defects are related to fracture initiation, stable propagation or final fracture. When choosing fracture toughness test data for use in engineering Fracture Mechanics-based assessments of energy pipelines, it is important to identify the stage of the fracture process and the expected fracture behavior in order to appropriately select test data that represent equivalent conditions. A mismatch between the physical fracture event being modeled and the chosen experimental fracture toughness data can result in unreliable predictions or overly conservative results. This paper presents a description of the physical fracture process, behavior and failure modes that pipelines commonly exhibit as they relate to fracture toughness testing, and their implications when evaluating cracks and cracks-like features in pipelines. Because pipeline operators, and practitioners of engineering Fracture Mechanics analyses, are often faced with the challenge of only having Charpy fracture toughness available, this paper also presents a review of the various correlations of Charpy toughness data to fracture toughness data expressed in terms of KIC or JIC. Considerations with the selection of an appropriate correlation for determining the failure pressure of pipelines in the presence of cracks and long-seam weld anomalies will be discussed.

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Nondestructive Estimation of Fracture Toughness Using Instrumented Indentation Technique

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.385-387.893 ◽

2008 ◽

Vol 385-387 ◽

pp. 893-896

Author(s):

Kyung Woo Lee ◽

Hyun Uk Kim ◽

Sang Wook Park ◽

Jung Suk Lee ◽

Kwang Ho Kim ◽

...

Keyword(s):

Fracture Toughness ◽

Damage Mechanics ◽

Volume Fraction ◽

Fracture Initiation ◽

Continuum Damage Mechanics ◽

Instrumented Indentation ◽

Initiation Point ◽

Indentation Technique ◽

Proposed Model ◽

Main Ideas

This study focused on the determination of fracture toughness by instrumented indentation technique. A theoretical model to estimate the fracture toughness of ductile materials is proposed and used to verify those results. Modeling of IIT to evaluate fracture toughness is based on two main ideas; the energy input up to characteristic fracture initiation point during indentation was correlated with material’s resistance to crack initiation and growth, and this characteristic fracture initiation point was determined by concepts of continuum damage mechanics. The estimated fracture toughness values obtained from the indentation technique showed good agreement with those from conventional fracture toughness tests based on CTOD. In addition, we confirmed that the proposed model can be also applied in the brittle material through modification of void volume fraction.

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Fatigue Crack Growth Rate and Fracture Toughness of API5L X65 in Sweet Environments

Volume 3: Materials Technology; Ocean Space Utilization ◽

10.1115/omae2013-10216 ◽

2013 ◽

Cited By ~ 1

Author(s):

Michael A. Tognarelli ◽

Ramgopal Thodla ◽

Steven Shademan

Keyword(s):

Fracture Toughness ◽

Growth Rate ◽

Fatigue Crack ◽

Crack Growth Rate ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Fatigue Crack Growth Rate ◽

Environmental Conditions ◽

Initiation Toughness ◽

Diffusible Hydrogen

Corrosion fatigue and fracture toughness in sour environments of APIX65 5L have typically been studied in relatively severe environments like NACE A and NACE B solutions. There are very limited data in sweet and mildly sour environments that are of interest in various applications. This paper presents fatigue crack growth frequency scans in a range of sweet and mildly sour environments as well as on different microstructures: Parent Pipe, Heat Affected Zone (HAZ) and Weld Center Line (WCL). The fatigue crack growth rate (FCGR) increased with decreasing frequency and reached a plateau value at low frequencies. FCGR in the sweet environments that were investigated did exhibit a frequency dependence (increasing with decreasing frequency) and had plateau FCGR in the range of 10–20× the in-air values. In the mildly sour environments that were investigated, FCGR was found to be about 25 to 30× higher than the in-air values. By comparison, in NACE A environments the FCGR is typically about 50× higher than the in-air values. The FCGRs of parent pipe and HAZ were found to be similar over a range of environments, whereas the WCL FCGR data were consistently lower by about a factor of 2×. The lower FCGR of the WCL is likely due to the lower concentration of diffusible hydrogen in the weld. FCGRs as a function of ΔK (stress integrity factor range) were measured on parent pipe at the plateau frequency. The measured Paris law curves were consistent with the frequency scan data. Rising displacement fracture toughness tests were performed in a range of sweet and sour environments to determine the R-curve behavior. Tests were performed in-situ at a slow K-rate of 0.05Nmm−3/2/s over a range of environmental conditions on parent pipe. The initiation toughness and the slope of the R-curve decreased sharply in the sour environments. The initiation toughness and slopes were largely independent of the notch location as well as environmental conditions. Typical values of initiation toughness were in the range of 90–110N/mm.

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