New Computational Procedures for Evaluation of Fracture Surfaces of the Drop Weight Tear Test of the Piping Steel

2011 ◽  
Author(s):  
Pavel Zˇidli´k ◽  
Petr Ferfecki ◽  
Bohumi´r Strnadel
Keyword(s):  
Fracture Surface ◽  
Ductile Fracture ◽  
Unstable Fracture ◽  
Fracture Surfaces ◽  
Drop Weight ◽  
Highly Sensitive ◽  
Drop Weight Tear Test ◽  
Computational Procedures ◽  
New Procedures

Drop weight tear test (DWTT) is one of the standard methods for evaluation of the ductility of large-dimensional structural components, such as pipelines used for gas and/or oil transportation. In general, the pipelines are even used in places with temperatures close to −40 °C, and in such environments, it is necessary to guarantee the resistance of the material used for pipeline against the initiation of unstable fracture. Currently, the percentage portion of the ductile fracture of the DWTT specimen is determined by an expert evaluator. The objective of this paper is to introduce new procedures working on the principle of deterministic, statistical and fractal description of the fracture surface. For the proposed computational procedures, the fracture surface of the test specimen is scanned at the macroscopic level using the 3D-Cam scanner. The newly investigated procedures show highly sensitive to the determination of the percentage portion of the ductile fracture on the tested DWTT specimens. The developed procedures to assess the fracture surfaces of the DWTT specimens contributes to making the results of this test more correct, objective and also increases the reliability and safety of the manufactured pipelines.

Flow Behaviour and Ductile Fracture Toughness of a High Toughness Steel

2004 ◽  
Author(s):  
S. Xu ◽  
R. Bouchard ◽  
W. R. Tyson
Keyword(s):  
Flow Stress ◽  
Ductile Fracture ◽  
Tensile Tests ◽  
Test Method ◽  
Opening Angle ◽  
Absorbed Energy ◽  
Crack Propagation Resistance ◽  
High Toughness ◽  
Drop Weight ◽  
Drop Weight Tear Test

This paper reports results of tests on flow and ductile fracture of a very high toughness steel with Charpy V-notch absorbed energy (CVN energy) at room temperature of 471 J. The microstructure of the steel is bainite/ferrite and its strength is equivalent to X80 grade. The flow stress was determined using tensile tests at temperatures between 150°C and −147°C and strain rates of 0.00075, 0.02 and 1 s−1, and was fitted to a proposed constitutive equation. Charpy tests were carried out at an initial impact velocity of 5.1 ms−1 using drop-weight machines (maximum capacity of 842 J and 4029 J). The samples were not broken during the test, i.e. they passed through the anvils after significant bending deformation with only limited crack growth. Most of the absorbed energy was due to deformation. There was little effect of excess energy on absorbed energy up to 80% of machine capacity (i.e. the validity limit of ASTM E 23). As an alternative to the CVN energy, the crack tip opening angle (CTOA) measured using the drop-weight tear test (DWTT) has been proposed as a material parameter to characterize crack propagation resistance. Preliminary work on evaluating CTOA using the two-specimen CTOA test method is presented. The initiation energy is eliminated by using statically precracked test specimens. Account is taken of the geometry change of the specimens (e.g. thickening under the hammer) on the rotation factor and of the effect of strain rate on flow stress.

Effect of Separation on Ductile Crack Propagation Behavior During Drop Weight Tear Test

2010 ◽  
Author(s):  
Takuya Hara ◽  
Taishi Fujishiro
Keyword(s):  
Crack Propagation ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
High Strength ◽  
Opening Angle ◽  
Ductile Crack ◽  
Line Pipe ◽  
Propagation Behavior ◽  
Drop Weight ◽  
Drop Weight Tear Test

The demand for natural gas using LNG and pipelines to supply the world gas markets is increasing. The use of high-strength line pipe provides a reduction in the cost of gas transmission pipelines by enabling high-pressure transmission of large volumes of gas. Under the large demand of high-strength line pipe, crack arrestability of running ductile fracture behavior is one of the most important properties. The CVN (Charpy V-notched) test and the DWTT (Drop Weight Tear Test) are major test methods to evaluate the crack arrestability of running ductile fractures. Separation, which is defined as a fracture parallel to the rolling plane, can be characteristic of the fracture in both full-scale burst tests and DWTTs. It is reported that separations deteriorate the crack arrestability of running ductile fracture, and also that small amounts of separation do not affect the running ductile fracture resistance. This paper describes the effect of separation on ductile propagation behavior. We utilized a high-speed camera to investigate the CTOA (Crack Tip Opening Angle) during the DWTT. We show that some separations deteriorate ductile crack propagation resistance and that some separations do not affect the running ductile fracture resistance.

An Experimental Study Evaluating Macroscopic Cavity Interactions as a Model of Microvoid Ductility

1996 ◽  
Vol 118 (4) ◽  
pp. 515-521 ◽  
Author(s):  
A. B. Geltmacher ◽  
P. Matic ◽  
D. P. Harvey
Keyword(s):  
Experimental Study ◽  
Fracture Surface ◽  
Ductile Fracture ◽  
Parametric Study ◽  
Longitudinal Axis ◽  
Surface Features ◽  
Fracture Surfaces ◽  
Model Studies ◽  
Load Displacement ◽  
Strength And Ductility

An experimental study of the interactions between macroscopic cavities was conducted. The goal was to determine simple cavity arrangements producing deformations similar to commonly observed features of ductile fracture. The production of cavity-centered fracture surface features and ligament thinning, representative of the type observed around and between microvoids on ductile fracture surfaces, were the specific objectives of this macroscopic study. The specimens employed were cylindrical tension specimens containing from one to six coplanar radial holes, with spherical end profiles, located at the center of the specimen and either zero or one cylindrical holelocated on the longitudinal axis of the specimen. The results of this parametric study identified the two specimens that best produced the desired features. The load-displacement results of these experiments also illustrate the effect of cavity geometry on the net strength and ductility of the array system. Specimens of these designs provide a future basis for simple and economical model studies of void interactions.

BRITTLE-DUCTILE TRANSITION AND SCALE DEPENDENCE: FRACTAL DIMENSION OF FRACTURE SURFACE OF MATERIALS

Fractals ◽  
1999 ◽  
Vol 07 (02) ◽  
pp. 159-168 ◽  
Author(s):  
TOSHITAKA IKESHOJI ◽  
TADASHI SHIOYA
Keyword(s):  
Fractal Dimension ◽  
Brittle Fracture ◽  
Fracture Surface ◽  
Ductile Fracture ◽  
Stress Triaxiality ◽  
Scale Dependence ◽  
Tensile Fracture ◽  
Scanning Electron Micrographs ◽  
Fracture Surfaces ◽  
Brittle Ductile Transition

The fractal dimension of fracture surfaces obtained within brittle-ductile transition regime is evaluated at various observation scales. Fracture surfaces are generated by the tensile fracture test. The brittle-ductile transition is accomplished by using the round-notched bar specimens with various notch radii, which cause the variation in stress triaxiality. The specimens are manufactured from mild steel, steel and cast-iron bar. The fracture model is identified according to the observation through scanning electron micrographs. The fractal dimension for ductile fracture surfaces is almost constant despite variations in observing scale and changes in stress triaxiality. Meanwhile, the fractal dimension on brittle fracture surfaces shows the different values for macroscopic and microscopic observing scales. This transition-like scale dependence of fractal dimension for brittle fracture surfaces is considered to reflect such a characteristic of the fracture i.e. its specific length in microscopic fracture mechanism. The existence of transition in fractal dimension with observing scale is considered to be an index, used to distinguish the ductile fracture surface from the brittle fracture one.

Analysis of Carbide Precipitates in API X80 Medium-Thickness Plate

2010 ◽  
Vol 146-147 ◽  
pp. 301-305
Author(s):  
Xiang Hua Kong ◽  
Shuai Wang ◽  
Yan Hui Sun ◽  
Jian Liang Zhang ◽  
Xiang Li ◽  
...  
Keyword(s):  
Fracture Surface ◽  
Cooling Rate ◽  
Thermal Simulation ◽  
Carbide Formation ◽  
Simulation Experiments ◽  
Medium Thickness ◽  
Drop Weight ◽  
Drop Weight Tear Test ◽  
Neutral Electrolyte

In order to discuss the abnormal fracture in drop weight tear test (DWTT) of API X80 medium-thickness plate, some unqualified samples in DWTT are characterized by SEM, AES, electrolysis and thermal simulation. SEM results show that there are many spherical precipitates in the fracture surface. EDS and AES results show that the abnormal spherical precipitates are carbides including Fe, Ni, Mo, Ti, etc. These precipitates can be extracted by neutral electrolyte method and their EDS results further demonstrate they are carbides. The formationmechanismof the precipitates is discussed based on thermal simulation experiments. When the cooling rate of medium-thickness plate is not enough high, especially in carbide formation area in Fe-C diagram, abnormal spherical carbides will occur and they are harmful for DWTT.

Experimental Study on Inverse Fracture in Drop-Weight Tear Test and Other Laboratory Test: Current Activities in HLP Committee, Japan, Report 2

2016 ◽  
Author(s):  
Tetsuya Tagawa ◽  
Taishi Fujishiro ◽  
Toshihiko Amano ◽  
Shuji Aihara ◽  
Satoshi Igi
Keyword(s):  
High Speed ◽  
Crack Arrest ◽  
Image Correlation ◽  
Correlation Technique ◽  
Brittle Crack ◽  
Fracture Surfaces ◽  
Drop Weight ◽  
Drop Weight Tear Test ◽  
Shear Area ◽  
The Impact

The drop-weight tear test (DWTT) has been widely used to evaluate the resistance of linepipe steels against long brittle fracture propagation. However, there is an ambiguity in its evaluation if the inverse fracture appears (100% shear area prior to cleavage fracture from the notch) on the DWTT fracture surfaces. Although cause of the inverse fracture is not fully understood, compressive pre-straining near the impact hammer has been discussed as a possible cause. In the present work, DWTTs for X65, X70 and X80 were performed. In addition to conventional DWTT specimen with a pressed notch (PN), PN specimen with a back slot and specimens with a chevron notch (CN) or a static pre-cracked (SPC) were examined. The fracture appearances were compared in the different strength and in the different initial notch type. The frequency of the inverse fracture appeared in these DWTTs were different in each material and each specimen type, but there were no cases free from the inverse fracture. The inverse fracture was investigated by fractography and the hardness profiles along the under layer of the fracture surfaces. Also, the strain histories during impact in DWTTs were measured by the digital image correlation technique based on the high-speed camera images. The DWTT specimen purpose is to evaluate the brittle crack arrestability of the material in a pressurized linepipe. The DWTT results should be examined with a manner of a running brittle crack in a pressurized linepipe. A large scale brittle crack arrest test, so called temperature gradient ESSO test was also performed for X65 mother plate. The shear area fraction measured in DWTT fracture appearance was compared with the local shear lip thickness fraction in ESSO test. The count of the inverse fracture was discussed in comparison with the long brittle crack arrest behavior in ESSO test.

Sign in / Sign up

Export Citation Format

Share Document