scholarly journals Ductile crack initiation and growth on a plasticized Polyvinylchloride during air bag deployment

2021 ◽  
Author(s):  
Lucien Laiarinandrasana ◽  
Clément Bertaux ◽  
Nicolas Amouroux ◽  
Cristian Ovalle Rodas
Keyword(s):  
Fracture Toughness ◽  
Crack Initiation ◽  
Crack Depth ◽  
Ductile Crack ◽  
Experimental Database ◽  
Plasticized Pvc ◽  
Element Simulation ◽  
Edge Notch ◽  
Scale Test ◽  
The One

With the goal of ensuring the security of passengers for automotive industry, the present work addresses the ductile fracture process of plasticized PVC. Dedicated clamped single edge notch bending (SENB) specimens were used to characterize the mechanisms of crack initiation and propagation for the studied material. The exploitation of the experimental database associated with finite element simulation of the crack propagation allowed, on the one hand, the calibration factor η p of this specific SENB specimen to be established, as a function of the crack depth ratio. On the other hand, the fracture toughness of the studied plasticized PVC was estimated to be 10.8 kJ/m 2 , value which was close to that reported in the literature for modified PVC. By using this fracture toughness value, a methodology aiming at the prediction of ductile crack initiation of the PVC skin integrated into a real dashboard (full scale test) was proposed.

Constraint Based Fracture Assessment of Seam-Welded Pipes Containing Axial Flaws

2006 ◽  
Author(s):  
Yuri Tkach ◽  
Anthony Horn ◽  
Adam Bannister ◽  
Edmund Bolton
Keyword(s):  
Fracture Toughness ◽  
Crack Depth ◽  
High Stress ◽  
Stress Triaxiality ◽  
Single Edge ◽  
Fracture Toughness Testing ◽  
Single Edge Notch ◽  
Seam Weld ◽  
Edge Notch ◽  
Toughness Testing

An Engineering Critical Assessment (ECA) of a pipeline containing an axial defect is usually conservative if standard fracture test pieces are used for the fracture toughness testing. Conventional fracture toughness testing standards employ specimens containing deep cracks in order to guarantee conditions leading to high stress triaxiality and crack-tip constraint. In the current work, single edge notch bend (SENB) and single edge notch tension (SENT) test specimens of two different a/W (crack depth/specimen width) ratios (0.15 and 0.6) were used to obtain HAZ fracture toughness of a seam weld. The influence of specimen geometry and a/W ratio on fracture toughness was investigated. The Master Curve methodology was employed to characterise HAZ fracture toughness of the seam weld in the ductile-to-brittle transition region. The reference temperature T0 was estimated using the test results obtained on specimens of different geometries and constraint levels. A series of ECAs of the pipe containing a surface axial flaw was performed and the benefits of a constraint based fracture mechanics analysis were demonstrated.

scholarly journals Considerations in selecting laboratory scale test specimens for evaluation of fracture toughness

2013 ◽  
Vol 4 (1) ◽  
Author(s):  
Matthias Verstraete ◽  
Stijn Hertelé ◽  
Koen Van Minnebruggen ◽  
Rudi Denys ◽  
Wim De Waele
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Test Specimen ◽  
Tensile Specimen ◽  
Full Scale ◽  
Laboratory Scale ◽  
Single Edge ◽  
Apparent Fracture Toughness ◽  
Edge Notch ◽  
Scale Test

  The assessment of defects in large steel structures requires a trustworthy evaluation of the material’s toughness. This toughness is not only a material property but is also influenced by the loading conditions and geometry; the so-called constraint. The resulting representative value is referred to as the apparent toughness. The evaluation of apparent fracture toughness in a flawed structure is preferentially performed through laboratory scale testing, as full scale tests are both expensive and often challenging to perform. Several laboratory scale test specimens are available, among which a Single Edge Notch Bending specimen, Single Edge Notch Tensile specimen, Double Edge Notch Tensile specimen and Centre Cracked Tensile specimen. Each of these specimens has its own specific constraint. Therefore, the selection of an appropriate test specimen is of primary importance for limiting the conservatism and avoiding potential unconservatism with respect to full scale behaviour. This paper provides a general framework to select an appropriate test specimen based on detailed finite element simulations of both the full scale structure and the laboratory scale test specimens. These finite element calculations allow for a characterization of the crack tip stress fields in both situations. Different theoretical frameworks are available for this characterization; theQ -parameter is considered in this paper. To demonstrate the applicability of this procedure, an example case is presented for circumferentially oriented defects in pressurized pipelines under longitudinal tension. It is concluded that the presented framework allows for efficiently selecting a laboratory scale test specimen, which enables to evaluate the apparent fracture toughness for a given large scale structure. The obtained toughness can thus be incorporated in analytical flaw assessment procedures, reducing the degree of conservatism. This in turn allows an economically effective design.

Fracture Toughness Variation With Flaw Depth in Various Specimen Geometries and Role of Constraint in Material Fracture Resistance

2017 ◽  
Author(s):  
Y. Hioe ◽  
S. Kalyanam ◽  
G. Wilkowski ◽  
S. Pothana ◽  
J. Martin
Keyword(s):  
Fracture Toughness ◽  
Crack Initiation ◽  
Crack Growth ◽  
Surface Crack ◽  
Crack Depth ◽  
Limit Load ◽  
Surface Cracks ◽  
Maximum Moment ◽  
Toughness Variation ◽  
Axial Surface

A series of pipe tests with circumferential surface cracks has been conducted along with fracture toughness tests using single-edge notch tension (SENT) specimens having similar crack depths and crack orientations as the surface-cracked pipes. This paper presents observation of measured fracture toughness variation due to the crack depth and discusses the effect of constraint on the material resistance to fracture. Crack-tip-opening displacement (CTOD) measurements were obtained with the use of a dual clip-gauge mounted on both the SENT specimens and center of the surface-cracks in the pipes. CTOD was obtained at both the crack initiation and during the crack growth through the ligament. CTOD is a direct measure of the material toughness in the pipe and SENT tests. CTOD at crack initiation and during crack growth can also be related to the material J-Resistance (J-R) curve. Commonly, the material resistance is assumed to be the same for all circumferential surface-crack geometries in a surface-cracked pipe fracture mechanics analyses. However, based on experimental observations on a series of recently conducted surface-cracked pipe tests, the CTOD at the center of the surface crack at the start of ductile tearing and maximum moment changed with the depth of the surface crack. This is believed to be a constraint effect on plasticity in the ligament which depends on crack depth. The CTOD values at crack initiation were decreasing linearly with crack depth. This linear decrease in CTOD trend with flaw depth was also observed in SENT tests. More importantly, the decrease in CTOD with surface crack depth was significant enough that the failure mode changed from being limit-load to elastic-plastic fracture even in relatively small-diameter TP304 stainless steel pipe tests. This toughness drop explains why the Net-Section-Collapse (limit-load) analysis overpredicted the maximum moment for some crack geometries, and why the deeper surface cracks tore through the pipe thickness at moments below that predicted by the NSC analysis for a through-wall crack of the same circumferential length. An “Apparent NSC Analysis” was developed in a companion paper to account for the changing toughness with crack depth [1]. Finally, this same trend in decreasing toughness with flaw depth is apparent in surface-cracked flat plates [2] and axial surface flaws in pipes [3]. The leak-before-break behavior for axial surface cracks is also not explained by numerical calculations of the crack-driving force when assuming the toughness is constant for all surface cracks and the through-wall cracks, but the change in toughness with surface flaw depth explains this behavior. Previously, axial flaw empirical limit-load solution was developed by Maxey and Kiefner [4], and is consistent with the observations from this paper.

scholarly journals Influence and evaluation of constraint on fracture toughness in pipeline research

2012 ◽  
Vol 3 (1) ◽  
pp. 25-35
Author(s):  
Matthias Verstraete ◽  
Stijn Hertelé ◽  
Wim De Waele ◽  
Rudi Denys
Keyword(s):  
Fracture Toughness ◽  
Full Scale ◽  
Small Scale ◽  
Width Ratio ◽  
Defect Tolerance ◽  
Edge Notch ◽  
Scale Test ◽  
Scale Structures ◽  
Tearing Resistance ◽  
Key Parameter

Accessing nowadays fossil fuel reserves requires a strain-based design approach. Within suchdesign, the ductile tearing resistance is a key parameter in assessing the defect tolerance. To determinethis tearing resistance, full scale (pressurized) tests can be performed. However, such approach would becostly and time consuming. Consequently, effort is made to select appropriate small scale test specimens.Most research has focused so far on the single edge notch bend (SENB) and tensile (SENT) specimen. Toevaluate the suitability of these test specimens, the crack tip stress fields can be examined or theresistance curves compared with full scale structures. This paper aims at comparing the trends observedusing these techniques. Furthermore, the suitability of the small scale test specimens is evaluated. It isconcluded that sufficiently long (length-to-width ratio equal to ten) clamped SENT specimens have thepotential to predict the tearing resistance of full scale pipes. In addition, the internal pressure does notsignificantly affect the fracture toughness. These conclusions are stated by both experimental results andfinite element simulations.

Fracture Control — Offshore Pipelines: Experimental Studies on the Effect of Crack Depth and Asymmetric Geometries on the Ductile Tearing Resistance

2005 ◽  
Author(s):  
Ba˚rd Nyhus ◽  
Erling O̸stby ◽  
Hans Olav Knagenhjelm ◽  
Scott Black ◽  
Per Arne Ro̸stadsand
Keyword(s):  
Fracture Toughness ◽  
Crack Depth ◽  
Experimental Studies ◽  
Single Edge ◽  
Offshore Pipelines ◽  
Ductile Tearing ◽  
Single Edge Notch ◽  
Edge Notch ◽  
Fracture Control ◽  
Tearing Resistance

Engineering critical assessment of offshore pipelines is usually very conservative if standardized single edge notch bend (SENB) specimens are used for the fracture mechanics testing. It is commonly accepted that the fracture toughness is dependent on the geometry constraint at the crack tip. The standardized SENB specimens have a high geometry constraint, and give lower bound fracture toughness for all geometries. For circumferential flaws in pipes the single edge notch tension (SENT) specimens is taken more into use, to establish more correct fracture toughness for the pipe in question. In this paper the effect of crack depth, misalignment and different wall thicknesses in SENT specimens have been studied. In addition the effect of crack depth and internal pressure in pipes have been studied with FE simulations.

Evaluation of the Lowest Temperature for Ductile Crack Initiation in an Irradiated RPV

2016 ◽  
Author(s):  
G. Wilkowski ◽  
F. W. Brust ◽  
M. Uddin ◽  
S. Kalyanam ◽  
V. Lacroix
Keyword(s):  
Fracture Toughness ◽  
Crack Initiation ◽  
Limit Load ◽  
Irradiation Damage ◽  
Ductile Crack ◽  
Irradiation Effects ◽  
Line Pipe ◽  
Gas Industry ◽  
Flaw Tolerance ◽  
Oil Gas

In this paper, work done for defining the lowest temperature for ductile fracture initiation in piping and fittings was extended to a sample reactor pressure vessel (RPV). The methodology used is called “Master Curve of Fracture Transition Temperatures” and was developed from correlations of thousands of laboratory tests and hundreds of pipe tests originally presented in 2005. Since then it has been extended to; low and high strength line-pipe steel base metals (oil/gas industry), blunt flaws as well as sharp cracks, girth welds for the oil/gas industry, fracture of pipe fittings/valves, and is the technical basis for the lowest temperature for ductile crack initiation in ferritic piping in Appendix C of ASME Section XI. Since the methodology is quite different than traditional approaches for nuclear component applications, the general methodology will be reviewed, as well as analysis results showing how surveillance capsule Charpy data could be used to predict the lowest temperature where ductile crack initiation would occur in RPVs. Once this temperature is established, then the upper-shelf toughness values can be used to determine if the failure is EPFM or limit-load, and the associated failure stresses. This temperature could be used for defining the pressure-temperature limits to assure that the RPV material has a high flaw tolerance. This methodology was proposed for the Doel 3 and Tihange 2 RPVs in Belgium. One key concern for operation of RPVs is determining the lowest operating temperature where ductile crack initiation is still expected which can be based on studies of irradiation effects on the measured toughness from Charpy tests of material in surveillance capsules. With ductile crack initiation the flaw tolerance is quite high even with long-term irradiation damage to the material. In fact, if the toughness is closer to limit-load than LEFM in a FAD analysis, then as long as there is ductile initiation, the irradiation effects increase the strength which could increase the flaw tolerance. There are some ongoing efforts within the ASME Section XI activities to define the minimum temperature where ductile initiation occurs in fracture toughness testing (typically based on a mixture of Charpy and 1T CT specimen data); however, there are still thickness and constraint effects on the fracture toughness for more precise application to a thick-walled vessel with a postulated axial surface crack.

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