A Review of Fracture Toughness Testing and Evaluation Using SENT Specimens

2014 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy
Keyword(s):  
Fracture Toughness ◽  
Test Procedure ◽  
Crack Tip ◽  
Test Methods ◽  
Fracture Toughness Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Test Standards ◽  
Resistance Curves ◽  
Crack Tip Constraint

Fracture toughness is an important material property in describing material resistance against fracture with a point value or in the format of a resistance curve. For ductile materials, the commonly used fracture parameters are the J-integral and the crack-tip opening displacement (CTOD, or δ). ASTM E1820 provides standard procedures for determining the JIc, δIc, J-R curve and δ-R curve using bending specimens with deep cracks. This usually leads to high crack-tip constraint conditions and conservative fracture resistance curves. Actual cracks found in pipelines and welds are often shallow and dominated by tensile forces, resulting in low constraint conditions and elevated resistance curves. Thus the standard resistance curves can be overly conservative for a shallow crack. To obtain realistic fracture toughness values to meet the practical needs for pipelines, different test methods have been developed using a single edge-notched tension (SENT) specimen. This includes the multiple specimen method, the single specimen method, the J-R curve test procedure, and the δ-R curve test procedure. This paper presents a critical technical review of existing fracture toughness test methods and procedures using SENT specimens, with discussions on the toughness estimation equation, key parameter calibration, rotation correction, and test procedure limitation. Historical efforts related to the SENT testing and applications of ASTM fracture test standards to the SENT specimens are also reviewed briefly.

Methods to Determine Low-Constraint Fracture Toughness: Review and Progress

2016 ◽  
Author(s):  
Xian-Kui Zhu
Keyword(s):  
Fracture Toughness ◽  
Test Methods ◽  
Standard Test ◽  
Initiation Toughness ◽  
Fracture Toughness Test ◽  
Crack Tip Opening Displacement ◽  
Test Procedures ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Low Constraint

Fracture toughness is often described by the J-integral or crack-tip opening displacement (CTOD) for ductile materials. ASTM, BSI and ISO have developed their own standard test methods for measuring fracture initiation toughness and resistance curves in terms of the J and CTOD using bending dominant specimens in high constraint conditions. However, most actual cracks are in low constraint conditions, and the standard resistance curves may be overly conservative. To obtain more realistic fracture toughness for actual cracks in low-constraint conditions, different fracture test methods have been developed in the past decades. To facilitate understanding and use the test standards, this paper presents a critical review on commonly used fracture toughness test methods using standard and non-standard specimens in reference to the fracture parameters J and CTOD, including (1) ASTM, BSI and ISO standard test methods, (2) constraint correction methods for formulating a constraint-dependent resistance curve, and (3) direct test methods using the single edge-notched tension (SENT) specimen. This review discusses basic concepts, basic methods, estimation equations, test procedures, historical efforts and recent progresses.

CTOD Specimen’s Fatigue Crack Prefabricated Test for Bridge Steel

2011 ◽  
Vol 71-78 ◽  
pp. 5034-5037
Author(s):  
Qi Ming Yu ◽  
Hao Liang Sa ◽  
Qian Long Yang ◽  
Pei Ao ◽  
Xiao Jing Liao ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Crack Tip ◽  
Fracture Toughness Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Toughness Test ◽  
Bridge Steel ◽  
Crack Tip Opening ◽  
Different Thickness

According to the BS7448 fracture toughness test standard and DNV-OS-C401,this dissertation conducted a CTOD(crack tip opening displacement) fatigue crack precast test with the used steel Q370qE in bridge.Respectively tested different thickness mather materials’condition of fatigue crack,and analysis the test’s results,thus obtained the related conclusions.

Review of Low-Constraint Fracture Resistance Testing With SENT Specimens

2014 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Tom McGaughy ◽  
Fabian Orth ◽  
Jon Jennings
Keyword(s):  
Fracture Resistance ◽  
Crack Tip ◽  
Test Methods ◽  
Resistance Testing ◽  
Resistance Curve ◽  
Single Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Resistance Curves ◽  
Low Constraint

Fracture resistance is an important material property and characterized by a J-integral resistance curve (J-R curve) or a crack-tip opening displacement (CTOD) resistance curve. ASTM standard specimens with deep cracks are subject to bending dominant forces, leading to high crack-tip constraint conditions and conservative fracture resistance curves. Actual cracks occurring in line pipes and welds are often shallow ones dominated by tensile forces, resulting in low constraint conditions. Shallow cracks have been shown to generate elevated fracture resistance curves in comparison to standard deep-crack results. To reduce the over-conservatism of standard resistance curves and to produce more realistic toughness properties to meet the needs of strain-based design approaches for pipelines, different procedures and technologies have been developed over the years to determine the low-constraint fracture resistance curves by use of the single edge-notched tension (SENT) specimens. This includes the multiple specimen method developed and standardized by DNV for J-R curve testing, the single specimen method developed by CanMet for J-R and CTOD-R curve testing, and the single-specimen method developed by ExxonMobil for CTOD-R curve testing. This paper delivers a technical review of existing fracture test methods using SENT specimens, and discusses the advantages and limitations of each method.

The Effects of In-Plane and Out-of-Plane Dimensions of a Curved Wide-Plate on Crack-Tip Constraint for Pipeline Fracture Assessment

2014 ◽  
Author(s):  
Hwee-Seung Lee ◽  
Nam-Su Huh ◽  
Ki-Seok Kim
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Tip ◽  
Standard Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Out Of Plane ◽  
Dimensional Finite Element ◽  
Crack Tip Constraint ◽  
Crack Tip Opening

One important element of fracture mechanics assessment in pipelines is how to determine the relevant fracture toughness (J-resistance or CTOD-resistance (crack-tip opening displacement)) for nonlinear fracture mechanics analysis. The general practice using a standard fracture mechanics specimen is known to often provide conservative estimates of toughness due to differences in crack-tip constraints between standard specimens and actual components. To improve the accuracy of predicting pipeline failure, various non-standard fracture mechanics specimens have been suggested over the past few decades. Among the several non-standard test specimens, a curved wide-plate in tension is often employed to predict fracture behavior of cracked components, for instance, in gas transportation pipelines. In order to show validity of a curved wide-plate in tension, the fracture toughness values from a full-scale pipeline test have been compared with those from a curved wide-plate in tension, and crack-tip constraints of a curved wide-plate in tension have also been compared with those of actual pipelines or other specimens during last decades. It is well known that a crack-tip constraint of test specimens, including curved wide-plates in tension, depends on many geometric and material parameters, for instance, crack length, thickness and width of specimen and material’s hardening characteristic. Thus, in order to obtain relevant fracture resistance from a curved wide-plate in tension representing accurate crack-tip constraint of pipeline of interest, variations of crack-tip constraints of curved wide-plates in tension according to various in-plane and out-of-plane constraint conditions should systematically be quantified. In the present study, systematic 3-dimensional finite element analyses attempt to investigate the effect of in-plane and out-of-plane parameters on crack-tip constraints of a curved wide-plate in tension.

Impact of Metallic Foam’s Microstructure to its Mechanical Property

2013 ◽  
Vol 634-638 ◽  
pp. 2808-2812
Author(s):  
Zhu Feng Sun ◽  
Ling Yun Xie
Keyword(s):  
Fracture Toughness ◽  
Cell Structure ◽  
Crack Tip ◽  
Metallic Foam ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Metal Material ◽  
Loading Mode ◽  
Foam Metal ◽  
Material Fracture

Explored the influence of pore structure of foam metal material on mechanical behavior of fracture. Discuss fracture toughness of several different micro geometric structure of foam metal material with finite element method. The author's calculations showed, microstructure and loading mode has an important effect on the fracture toughness of the foam metal material. due to ignoring the effects of cell structure on the mechanical properties of materials, the classic fracture toughness criterion -crack tip opening displacement (COD) is incomplete, it would be more efficient to take opening displacement change rate of the crack-tip as the parameter to characteristic the metallic foam material fracture toughness.

Experimental Study on CTOD Fracture Toughness of Welded Joints of Low Temperature Steel

2011 ◽  
Vol 328-330 ◽  
pp. 1272-1276 ◽  
Author(s):  
Zong Tao Fang ◽  
Bo Sun ◽  
Chun Run Li
Keyword(s):  
Fracture Toughness ◽  
Low Temperature ◽  
Welded Joints ◽  
Welding Process ◽  
Offshore Platform ◽  
Fracture Toughness Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Welding Procedure ◽  
Crack Tip Opening

According to BS7448 fracture toughness test standard, crack tip opening displacement (CTOD) for ASTM A333 Gr.6 low temperature steel which is used in offshore platform were carried out in low temperature (0°C, -29°C). Three point bending tests were conducted on the specimens, the dimension of which is B×2B (B is the thickness) and notch direction is NP. The final value of CTOD was calculated by P-V curves of both the welds and HAZ (heat affected zone). And the experimental results were analyzed and discussed in the paper. The low temperature steel welded joints show good low temperature toughness, the selected welding procedure is applied to construction of pipelines.The CTOD value of HAZ is larger than weld metal and weld is the weakest position in the whole structure. The experiment results provide an important basis for the choice of welding method and welding process parameters, ECA assessment and construction of offshore platform.

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