Comparison Between Standard and Modified Back-Slotted DWTT Specimens

2014 ◽  
Author(s):  
Do-Jun Shim ◽  
Mohammed Uddin ◽  
Gery Wilkowski ◽  
Da-Ming Duan ◽  
James Ferguson
Keyword(s):  
Ductile Fracture ◽  
Fracture Resistance ◽  
Cohesive Zone Model ◽  
Crack Arrest ◽  
Zone Model ◽  
Line Pipe ◽  
Static Test ◽  
Drop Weight Tear Test ◽  
Major Factors ◽  
The Impact

The effect of fracture speed on the ductile fracture resistance of line-pipe steels can have an important effect in the basic understanding of the toughness requirements for crack arrest. Recently, the authors have extended the drop-weight tear test (DWTT) work and developed a modified back-slot (MBS) DWTT specimen to obtain higher fracture speeds. The initial experimental observations demonstrated that this type of specimen can be used to obtain higher fracture speeds. Furthermore, the experimental results clearly showed the effect of fracture speed on the ductile fracture resistance. In this paper, an in-depth study was carried out to further investigate why higher fracture speeds are obtained in the MBS-DWTT specimens. For this purpose, quasi-static and dynamic/impact DWTT experiments were conducted for both standard DWTT and MBS-DWTT specimens. In addition, finite element analyses using cohesive zone model were carried out to investigate the fracture behavior in these tests. In summary, the higher fracture speeds in the MBS-DWTT come from two major factors. First, as demonstrated by the quasi-static test results, the natural unloading characteristics of the MBS-DWTT specimen (even under pure displacement-controlled loading) leads to higher fracture speeds. Second, the steep unloading curve of the MBS-DWTT specimen produces a higher possibility of an unstable ductile fracture even during the impact event, which will result in higher fracture speeds.

Effect of Fracture Speed on Ductile Fracture Resistance: Part 1—Experimental

2010 ◽  
Author(s):  
Do-Jun Shim ◽  
Gery Wilkowski ◽  
Da-Ming Duan ◽  
Joe Zhou
Keyword(s):  
Steady State ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
State Energy ◽  
Crack Arrest ◽  
Experimental Results ◽  
Displacement Curve ◽  
Charpy Test ◽  
Line Pipe ◽  
Drop Weight Tear Test

The effect of fracture speed on the ductile fracture resistance of line-pipe steels can have an important effect in the basic understanding of the toughness requirements for crack arrest. Over the last few decades, it has become recognized that the drop-weight tear test (DWTT) better represents the ductile fracture resistance than the Charpy test since it utilizes a specimen that has the full thickness of the pipe and has a fracture path long enough to reach steady-state fracture resistance. However, the fracture speed in the DWTT is typically 50 to 60 feet per second (15.2 to 18.3 m/s), whereas the fracture speed in the full-scale pipe test is 300 to 1,000 fps (91.4 to 305 m/s). Recently, the authors have extended the DWTT work and developed a modified back-slot DWTT specimen to obtain higher fracture speeds. One aspect of this modified specimen was to increase the width of DWTT sample from the standard 3-inch (76.2 mm) to 5-inch (127 mm). This was done to increase the ligament length in a relatively deep back-slotted specimen to capture more steady-state data. The initial experimental results demonstrated that this type of specimen can be used to obtain higher fracture speeds. Furthermore, the experimental results clearly showed the effect of fracture speed on the ductile fracture resistance. In this paper, to extend the work on modified back-slot DWTT specimens, the tup was instrumented to measure the load during dynamic impact. From this, the load-displacement curve, steady-state energy (or energy per area) was obtained for the modified back-slot DWTT specimens. These results were compared to those obtained from the standard 3-inch specimens. These results also clearly showed the effect of fracture speed on fracture resistance.

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.

scholarly journals Rate-Dependent Cohesive Zone Model for Fracture Simulation of Soda-Lime Glass Plate

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 749 ◽  
Author(s):  
Dong Li ◽  
Demin Wei
Keyword(s):  
Strain Rate ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Glass Plate ◽  
Soda Lime ◽  
Soda Lime Glass ◽  
Zone Model ◽  
Rate Dependent ◽  
Fracture Simulation ◽  
The Impact

In this paper, rate-dependent cohesive zone model was established to numerical simulate the fracture process of soda-lime glass under impact loading. Soda-lime glass is widely used in architecture and automobile industry due to its transparency. To improve the accuracy of fracture simulation of soda-lime glass under impact loading, strain rate effect was taken into consideration and a rate-dependent cohesive zone model was established. Tensile-shear mixed mode fracture was also taken account. The rate-dependent cohesive zone model was implemented in the commercial finite element code ABAQUS/Explicit with the user subroutine VUMAT. The fracture behavior of a monolithic glass plate impacted by a hemispherical impactor was simulated. The simulation results demonstrated that the rate-dependent cohesive zone model is more suitable to describe the impact failure characteristics of a monolithic glass plate, compared to cohesive zone model without consideration of strain rate. Moreover, the effect of the strain rate sensitivity coefficient C, the mesh size of glass plate and the impact velocity on the fracture characteristics were studied.

Effects of Soil Cohesiveness and Depth on Dynamic Ductile Fracture Speeds

2008 ◽  
Author(s):  
D. Rudland ◽  
D.-J. Shim ◽  
G. M. Wilkowski ◽  
S. Kawaguchi ◽  
N. Hagiwara ◽  
...  
Keyword(s):  
Ductile Fracture ◽  
Large Scale ◽  
Soil Depth ◽  
Crack Arrest ◽  
Small Scale ◽  
Total Density ◽  
Pipe Material ◽  
Pipe Steels ◽  
Line Pipe ◽  
Fracture Arrest

The ductile fracture resistance of newer line pipe steels is of concern for high grade/strength steels and higher-pressure pipeline designs. Although there have been several attempts to make improved ductile fracture arrest models, the model that is still used most frequently is the Battelle Two-Curve Method (TCM). This analysis incorporates the gas-decompression behavior with the fracture toughness of the pipe material to predict the minimum Charpy energy required for crack arrest. For this analysis, the influence of the backfill is lumped into one empirically developed “soil” coefficient which is not specific to soil type, density or strength. No attempt has been made to quantify the effects of soil depth, type, total density or strength on the fracture speeds of propagating cracks in line pipe steels. In this paper, results from small-scale and large-scale burst tests with well-controlled backfill conditions are presented and analyzed to determine the effects of soil depth and cohesiveness on the fracture speeds. Combining this data with the past full-scale burst data used in generating the original backfill coefficient provides additional insight into the effects of the soil properties on the fracture speeds and the arrest of running ductile fractures in line pipe materials.

An Improved Contact Formulation for Impact Crack Simulations in a Laminated Glass Beam

2018 ◽  
Vol 15 (08) ◽  
pp. 1850077 ◽  
Author(s):  
Shunhua Chen ◽  
Mengyan Zang ◽  
Shinobu Yoshimura ◽  
Zumei Zheng
Keyword(s):  
Cohesive Zone Model ◽  
Main Idea ◽  
Numerical Approach ◽  
Zone Model ◽  
Laminated Glass ◽  
Contact Formulation ◽  
Before And After ◽  
Numerical Instabilities ◽  
The Impact ◽  
Glass Beam

Laminated glass is a simple sandwiched structure, which, however, is widely used in automotive and architectural industries. The well-known extrinsic cohesive zone model has proved to be a powerful numerical approach for the glass-ply crack simulations in laminated glass, where the classical node-to-segment contact treatment is usually employed. However, an unphysical phenomenon, named contact force jump, may arise during crack simulations, thereby resulting in numerical instabilities or incorrect simulation results. To address this issue, we develop an improved node-to-segment contact formulation to make the contact interactions in extrinsic crack simulations more stable. The main idea is to keep the number of contact constraints constant before and after cracking. The improved contact formulation is very simple and easy to implement, which, however, is effective to address the unphysical phenomenon. Three numerical examples, including the impact crack simulations of a laminated glass beam, are performed to validate the accuracy and effectiveness of the improved contact formulation.

Fast Ductile Fracture: Dependence of Propagation Resistance on Crack Velocity

2018 ◽  
Author(s):  
Chris Bassindale ◽  
Xin Wang ◽  
William R. Tyson ◽  
Su Xu
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Crack Velocity ◽  
Cohesive Zone Model ◽  
Pipeline Steel ◽  
Mass Density ◽  
Opening Angle ◽  
Zone Model ◽  
Plate Model ◽  
Line Pipe

In this paper, the effect of inertia on the steady-state velocity of a propagating crack in a modern high toughness pipeline steel was investigated. The line pipe steel examined in this work was an American Petroleum Institute (API) Standard X70 steel. A tensile plate model, simplified from the geometry of a pipe, was studied using the finite element code ABAQUS 6.14-2. The cohesive zone model (CZM) was used to simulate crack propagation. The CZM parameters were calibrated based on matching the crack tip opening angle (CTOA) measured from a drop-weight tear test (DWTT) finite element model to the experimental CTOA of the material. The CZM parameters were then applied to the tensile plate model. The effect of inertia on the steady-state crack velocity was systematically assessed by altering the density of the material used with the plate model. To isolate the influence of inertia, the effect of strain rate on the fracture process and material plasticity was neglected. The results of this study demonstrate that the steady-state crack velocity was affected by the density of the material. The steady-state crack velocity was reduced with increasing mass density, as demonstrated by the effect of backfill. Furthermore, it was shown that the CTOA extracted from the CZ model was not affected by the density of the model.

Effect of Notch Type in Drop-Weight Tear Test Specimen on Crack Propagation and Arrest Behavior

2018 ◽  
Author(s):  
Satoshi Igi ◽  
Toshihiko Amano ◽  
Takahiro Sakimoto ◽  
Yasuhiro Shinohara ◽  
Tetsuya Tagawa
Keyword(s):  
Crack Propagation ◽  
Large Scale ◽  
Crack Arrest ◽  
Brittle Crack ◽  
Chevron Notch ◽  
Drop Weight ◽  
Drop Weight Tear Test ◽  
Shear Area ◽  
The Impact ◽  
Crack Propagation And Arrest

The drop-weight tear test (DWTT) has been widely used to evaluate the resistance of linepipe steels against brittle fracture propagation. However, in the recent years there is an ambiguity in its evaluation if inverse fracture appears on the specimen fracture surfaces. Although cause of the inverse fracture is not fully understood, compressive pre-straining near the impact hammer and existing tiny split have been discussed as a possible cause. In this paper, machined notch in brittle weld DWTT for X65 was performed and compared with various notch types of DWTTs such as conventional DWTT specimen with a pressed notch (PN), a chevron notch (CN) and a static pre-cracked (SPC). The fracture appearances were compared with different strength X65 - X80 grades linepipes and with different initial notch types. The frequency of the inverse fracture appeared in these DWTTs were different in each material and each specimen types, but there were no cases where the inverse fracture did not occurs. The purpose of DWTT is to evaluate the brittle crack arrestability of the material in a pressurized linepipe. A large scale brittle crack arrest test, so called West Jeferson test is generally used to reproduce crack propagation and arrest behavior in an actual pipeline material. A middle scale test so called Crack Arrest Temperature (CAT) test was also proposed to check the shear area fraction measured in DWTT with API rating with that the local shear lip thickness fraction in those tests. CAT test can well reproduce crack propagation and arrest behavior under the condition of brittle crack initiation from the initial notch.

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