Determination of CTOD Resistance Curves in SENT Specimens With a Tilted Notch

2014 ◽  
Author(s):  
Koen Van Minnebruggen ◽  
Matthias Verstraete ◽  
Rudi Denys ◽  
Philippe Thibaux ◽  
Wim De Waele
Keyword(s):  
Crack Opening ◽  
Potential Drop ◽  
Element Model ◽  
Image Correlation ◽  
Pure Mode ◽  
Opening Displacement ◽  
Thermo Electric ◽  
Seam Weld ◽  
Tearing Resistance

The Single Edge Notched Tension (SENT) specimen is a common tool for the determination of tearing resistance in pipeline steels and welds. However, it assumes pure mode I crack tip loading, which is unrepresentative for the evaluation of spiral seam weld flaws. To this purpose, the authors have performed SENT tests using specimens with a tilted notch. This paper evaluates experimental techniques to obtain the tearing resistance of such specimens. Mixed-mode crack opening displacement and ductile tearing are successfully measured using digital image correlation and direct current potential drop, respectively. The latter technique involves a calibration on the basis of a thermo-electric finite element model. Tearing resistance tends to increase with increasing notch tilt angle. Based on the limited number of tests performed, tilted notch SENT testing appears to be a promising tool for the assessment of spiral seam weld flaws.

Determination of Ductile Tearing Resistance Curve in Weld Joints

2009 ◽  
Author(s):  
S. Marie ◽  
P. Gilles ◽  
P. Ould
Keyword(s):  
Welded Joints ◽  
Opening Displacement ◽  
Weak Point ◽  
Global Parameter ◽  
Ductile Tearing ◽  
Weld Joints ◽  
Resistance Curves ◽  
Reliable Solution ◽  
Tearing Resistance

Steels present in the ductile domain a tearing resistance which increase with the crack propagation up to the failure. This ductile tearing resistance is in general characterised with curves giving the variation of a global parameter (opening displacement at the crack tip δ, integral J) versus the crack extension Δa. These global approaches depend more or less on the specimen geometry and on the type of the imposed loading. Local approaches based on the description of the ductile tearing mechanisms provide reliable solution to the transferability problem (from the lab specimen to the component) but are complex and costly to use and are not codified. These problems get worse in the case of a weld joint where no standard is available for the measurement of their ductile tearing resistance. But the welded joints are often the weak point of the structure because of greater risk of defects, the heterogeneity of the microstructure of the weld, deformation along the interface between two materials with different yield stress (mismatch).... After briefly recalling the problems of transferability of the ductile tearing resistance curves obtained on lab specimen to the case of components, this article identifies the factors complicating the determination of the toughness in the welded joints and gives recommendations for the experimental determination of ductile tearing resistance curves of welded joints.

scholarly journals The Use of the Acoustic Emission Method to Identify Crack Growth in 40CrMo Steel

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2140 ◽  
Author(s):  
Aleksandra Krampikowska ◽  
Robert Pała ◽  
Ihor Dzioba ◽  
Grzegorz Świt
Keyword(s):  
Acoustic Emission ◽  
Brittle Fracture ◽  
Crack Growth ◽  
Crack Opening ◽  
Potential Drop ◽  
Growth Stages ◽  
Opening Displacement ◽  
Engineering Structures ◽  
Cracking Process ◽  
Ae Signals

The article presents the application of the acoustic emission (AE) technique for detecting crack initiation and examining the crack growth process in steel used in engineering structures. The tests were carried out on 40CrMo steel specimens with a single edge notch in bending (SENB). In the tests crack opening displacement, force parameter, and potential drop signal were measured. The fracture mechanism under loading was classified as brittle. Accurate AE investigations of the cracking process and SEM observations of the fracture surfaces helped to determine that the cracking process is a more complex phenomenon than the commonly understood brittle fracture. The AE signals showed that the frequency range in the initial stage of crack development and in the further crack growth stages vary. Based on the analysis of parameters and frequencies of AE signals, it was found that the process of apparently brittle fracture begins and ends according to the mechanisms characteristic of ductile crack growth. The work focuses on the comparison of selected parameters of AE signals recorded in the pre-initiation phase and during the growth of brittle fracture cracking.

Determination of J-Integral Using the Load-COD Record for Circumferential Through-Wall Cracked Pipes

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Nam-Su Huh ◽  
Yun-Jae Kim
Keyword(s):  
Crack Opening ◽  
Estimation Method ◽  
J Integral ◽  
Opening Displacement ◽  
Element Analysis ◽  
Load Line ◽  
Load Line Displacement ◽  
Η Factor ◽  
J Estimation

The present paper provides experimental J estimation equation based on the load-crack opening displacement (COD) record for testing the circumferential through-wall cracked pipe under combined tension and bending. Based on the limit analysis and the kinematically admissible rigid-body rotation field, the plastic η-factor for the load-COD record is derived and is compared with that for the load-load line displacement record. Comparison with the J results from detailed elastic-plastic finite element analysis shows that the proposed method based on the load-COD record provides reliable J estimates even for shallow cracks (small crack angle), whereas the conventional approach based on the load-load line displacement record gives erroneous results for shallow cracks. Thus, the proposed J estimation method could be recommended for testing the circumferential through-wall cracked pipe, particularly with shallow cracks.

Comparison of J-Integral Measurement Methods on Clamped Single-Edge Notched Tension Specimens

2016 ◽  
Author(s):  
Timothy S. Weeks ◽  
Jeffrey W. Sowards ◽  
Ross A. Rentz ◽  
David T. Read ◽  
Enrico Lucon
Keyword(s):  
Mouth Opening ◽  
Surface Strain ◽  
Image Correlation ◽  
Crack Mouth Opening Displacement ◽  
J Integral ◽  
Crack Mouth ◽  
Single Edge ◽  
Opening Displacement ◽  
Strain Gradients

This paper reports an extension of a previous study that compared methods of evaluating J by the crack mouth opening displacement and by surface strain gradients. Here, the surface strain gradients are measured by three-dimensional digital image correlation. The results herein represent a small test matrix that involved evaluation of the J-integral for clamped single-edge notched tensile specimens from API 5L X65 base-metal, weld metal and the adjacent heat affected zone; the J-integral was evaluated by a standardized procedure utilizing the crack mouth opening displacement (CMOD) and by the contour integral method on an external surface strain contour. Digital image correlation provides sufficient full-field strain data for use by this method and is considerably more robust than surface-mounted strain gage instrumentation. A series of validity checks are presented that demonstrate that the data are useful and valuable. Experimental determination of the J-integral is not limited to thoroughly analyzed test geometries and may be achieved with limited instrumentation. Furthermore, the method described does not require a determination of crack size nor any instrumentation that requires access to the crack mouth.

Determination of crack-opening displacement by the method of caustics

1974 ◽  
Vol 9 (3) ◽  
pp. 197-205 ◽  
Author(s):  
P S Theocaris
Keyword(s):  
Crack Opening Displacement ◽  
Mechanical Characteristics ◽  
Crack Opening ◽  
Crack Tip ◽  
External Loading ◽  
Small Scale ◽  
Opening Displacement ◽  
Cracked Plates ◽  
Good Agreement

A new experimental technique based on the method of caustics is presented for the measurement of the distance between the lips of a crack near the crack-tip. The two parts of the caustic formed by reflections from the front and rear faces of the specimen lie at a distance from each other. The gap between these parts depends on the total c.o.d. (crack-opening displacement), that is the initial opening and the opening due to loading, as well as on the optical and mechanical characteristics of the material By increasing the external loading of the cracked plate, the gap between the parts of the caustic was changed and this gap measured the instantaneous c.o.d. due to loading. The method was applied to the measurement of small c.o.d.s. due to small-scale loading, with satisfactory results. Therefore it can certainly be used to measure c.o.d.s at large loading steps, up to fracture, because the gap between the parts of the caustic becomes significant and easy to measure. Measurements with cracked plates made of p.m.m.a. (polymethylmethacrylate) and polycarbonate showed that the results obtained are in good agreement with theory. Thus, it has been proved that the method of caustics yields a very sensitive means for measuring c.o.d.s, especially in small-scale deformations, where measurement of c.o.d by conventional methods is inaccurate. A great advantage of the method is that it measures the c.o.d.s at a well defined region, which always remains near to the crack tip.

scholarly journals R-curve evaluation of pipeline girth welds using advanced measurement techniques

2014 ◽  
Vol 5 (1) ◽  
pp. 10
Author(s):  
Nick Geldhof ◽  
Joeri Van Iseghem ◽  
Matthias Verstraete ◽  
Stijn Hertelé ◽  
Koen Van Minnebruggen ◽  
...  
Keyword(s):  
Crack Extension ◽  
Measurement Techniques ◽  
Potential Drop ◽  
Image Correlation ◽  
Assessment Procedure ◽  
Full Field ◽  
Resistance Curves ◽  
Unloading Compliance ◽  
Girth Welds ◽  
Tearing Resistance

A strain-based flaw assessment procedure is recommended for girth welded pipelines subjected to large deformations. To evaluate the allowable defect dimensions, the tearing resistance needs to be characterized. This paper investigates the effect of weld metal strength mismatch on the resistance curve using Single Edge Notched Tension (SENT) specimens. Several advanced measurement techniques are applied during the tests in order to obtain a continuous measurement of crack extension and to visualize the deformation fields near the crack. The resistance curves are determined using a single specimen technique. The unloading compliance method and the potential drop method result in similar predictions of ductile crack extension, yielding similar resistance curves. Next to these measurements, the full field deformations are determined using digital image correlation. The experiments indicate that the position of the applied notch in the weld has the potential to influence the strain fields.

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