Numerical Analysis of Constraint and Strength Mismatch Effects on Local Fracture Resistance of Bimetallic Joints

2015 ◽  
Vol 750 ◽  
pp. 24-31 ◽  
Author(s):  
Kai Fan ◽  
Guo Zhen Wang ◽  
Jie Yang ◽  
Fu Zhen Xuan ◽  
Shan Tung Tu
Keyword(s):  
Crack Growth ◽  
Fracture Resistance ◽  
Crack Depth ◽  
Stress Triaxiality ◽  
Local Stress ◽  
Crack Growth Resistance ◽  
Specimen Thickness ◽  
Local Fracture ◽  
Out Of Plane ◽  
Crack Tips

In this paper, the finite element method (FEM) based on GTN model was used to investigate the in-plane/out-of-plane constraint and strength mismatch effects on local fracture resistance of A508/Alloy52Mb bimetallic joint. The J-resistance curves, crack growth paths and local stress-stain distributions in front of crack tips were calculated for cracks with different constraints and strength mismatches. The results show that the local fracture resistance of the interface crack in this joint is sensitive to constraint and strength mismatch effects. With increasing in-plane constraint (crack depth a/W), out-of-plane constraint (specimen thickness B) and strength mismatch degree, the plastic strain and stress triaxiality around crack tip increase, and the corresponding crack growth resistance decreases. The crack with strength mismatch factor M=1 displays a markedly higher crack growth resistance than the other cracks with M>1 and M<1. It also has been found that there is an interaction between in-plane/out-of-plane constraint and strength mismatch for the bimetallic joint. With increasing in-plane/out-of-plane constraint, strength mismatch effect on fracture toughness becomes weaken. For accurate and reliable safety design and failure assessment of the bimetallic joint structures, the effects of constraint and strength mismatch on local fracture resistance need to be considered.

Numerical Study of the Crack-Front Constraint for SENT Specimens of X80 Pipeline Steel

2017 ◽  
Vol 898 ◽  
pp. 735-740
Author(s):  
Ting Zhong ◽  
Lin Zhu ◽  
Yan Zhou ◽  
Jian Shuai ◽  
Lan He
Keyword(s):  
Crack Front ◽  
Numerical Study ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Stress Triaxiality ◽  
Width Ratio ◽  
Specimen Thickness ◽  
X80 Pipeline Steel ◽  
Specimen Width ◽  
Average Measure

This work presents a numerical study of crack-front constraint for SENT specimens of X80 pipeline steel, to examine geometry effect on the correlation of crack-front stress field and constraint. An average measure of constraint over crack-front Am was employed to characterize the crack-front constraint. SENT specimens with varying geometries (different crack depth to specimen width ratio, a/W, and different specimen width and thickness, W/B) were analyzed by Gurson-Tvergaard-Needleman model (GTN model). Results showed that the stress triaxiality Am can characterize the crack-front constraint of X80 pipeline steel very well. The level of the Am-△a curve rises with the decrease of crack depth, and increases first and then decreases with the increase of SENT specimen thickness.

A Fracture Mechanics Investigation on Crack Growth in Massive Forming

2005 ◽  
Vol 482 ◽  
pp. 339-342 ◽  
Author(s):  
Gernot Trattnig ◽  
Christof Sommitsch ◽  
Reinhard Pippan
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Hydrostatic Stress ◽  
Crack Opening ◽  
Crack Depth ◽  
High Stress ◽  
Symmetry Plane ◽  
Stress Triaxiality ◽  
Opening Displacement ◽  
Massive Forming

To understand the crack growth in massive forming and to consequentially avoid crack growth in workpieces, it is necessary to investigate its dependence on the crack depth and thus on the state of hydrostatic stress. Prior work shows that the crack opening displacement (COD) for shallow cracked tension specimens with low stress triaxiality is twice as high as for deep cracked specimens with high stress triaxiality. This work examines the crack growth in compression specimens with pre-cracked cylindrical upsetting samples. The compression samples were cut in the stress symmetry plane in order to observe crack initiation and crack growth by a single specimen technique. In this way it is possible to observe blunting, crack initiation and crack growth inside the upsetting specimens. The resulting COD does not differ significantly from the values achieved in tension samples with short surface cracks.

Experimental determination of crack growth resistance of ductile materials

1981 ◽  
Vol 16 (2) ◽  
pp. 123-126 ◽  
Author(s):  
C W Woo ◽  
M D Kuruppu
Keyword(s):  
Crack Growth ◽  
Fracture Resistance ◽  
Test Specimen ◽  
Stable Crack Growth ◽  
Crack Growth Resistance ◽  
Large Structure ◽  
Ductile Materials ◽  
Comparison Results ◽  
Static Energy

A method of determining the fracture resistance of ductile materials is presented in this paper. The method employs a renforced DCB test specimen to characterize stable crack growth in a large structure. From the consideration of the quasi-static energy balance during slow stable crack growth, the fracture resistance was measured using the J approach. By repeated partial unloading during slow stable crack growth the need for multiple specimens with virgin crack length was eliminated. The fracture resistance of three different materials was measured for comparison. Results indicated that the fracture resistance increases significantly during the nitial stage of crack growth. When the crack propagation reaches an equilibrium state of stable crack growth the fracture resistance remains fairly constant over a large crack increment.

Axisymmetric Modeling of Constraint Effect on the Ductile Crack Growth Resistance of Circumferentially Cracked Pipes

2010 ◽  
Author(s):  
Jie Xu ◽  
Zhiliang Zhang ◽  
Erling O̸stby ◽  
Ba˚rd Nyhus ◽  
Dongbai Sun
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Volume Fraction ◽  
Crack Depth ◽  
Crack Growth Resistance ◽  
Good Representation ◽  
Ductile Crack ◽  
Single Edge ◽  
Ductile Crack Growth ◽  
Senb Specimen

Ductile crack growth plays an important role in the analysis of the fracture behavior of structures. Crack-like defects in pipe systems often develop during fabrication or in-service operation. The standard single edge notched bending (SENB) specimen with crack depth of a/W = 0.5 has a significantly higher geometry constraint than actual pipes with circumferential surface cracks, which therefore introduces a high degree of conservatism in engineering critical assessment (ECA) of pipes. Moreover, it is difficult to know how conservative the results are, because the geometry constraint is highly material-dependent. For circumferential surface flaws in pipes, the single edge notched tension (SENT) specimen has frequently been used because it has a geometry constraint in front of the crack tip that is similar to the cracks in pipes. Much work has been carried out on tensile testing for the SENT specimen as an alternative fracture mechanics specimen of pipes. In studying fully circumferential cracks in pipes, the crack geometry, applied load and boundary conditions are symmetrical about the axis of revolution. A typical radial plane containing the axis of rotational symmetry can represent these axisymmetric bodies; therefore the three-dimensional analysis can be reduced to a two-dimensional problem. This work systemically applies 2D axisymmetric models to study the ductile crack growth behavior of pipes with fully internal and external circumferential cracks under large scale yielding conditions. The complete Gurson model (CGM) developed and implemented by Zhang was utilized to predict the ductile crack growth resistance curves. Pipes with various internal pressure, diameter-to-thickness ratios, crack depths and material properties, as denoted by hardening and initial void volume fraction, have been analyzed. The results have been compared with those of corresponding clamped-loaded SENT (with same crack depth) and standard SENB specimens. It clearly indicates that the SENT specimen is a good representation of circumferentially flawed pipes and an alternative to the conventional standard SENB specimen for the fracture mechanics testing in ECA of pipes.

scholarly journals Numerical Investigation of Strength Mismatch Effect on Ductile Crack Growth Resistance in Welding Pipe

2020 ◽  
Vol 10 (4) ◽  
pp. 1374
Author(s):  
Lin Su ◽  
Jie Xu ◽  
Wei Song ◽  
Lingyu Chu ◽  
Hanlin Gao ◽  
...  
Keyword(s):  
Crack Growth ◽  
Fracture Resistance ◽  
Crack Growth Resistance ◽  
Ductile Crack ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Ductile Crack Growth ◽  
Welding Pipe ◽  
Resistance Curves

The effect of strength mismatch (ratio between the yield stress of weld metal and base metal, My) on the ductile crack growth resistance of welding pipe was numerically analyzed. The ductile fracture behavior of welding pipe was determined while using the single edge notched bending (SENB) and single edge notched tension (SENT) specimens, as well as axisymmetric models of circumferentially cracked pipes for comparison. Crack growth resistance curves (as denoted by crack tip opening displacement-resistance (CTOD-R curve) have been computed using the complete Gurson model. A so-called CTOD-Q-M formulation was proposed to calculate the weld mismatch constraint M. It has been shown that the fracture resistance curves significantly increase with the increase of the mismatch ratio. As for SENT and pipe, the larger My causes the lower mismatch constraint M, which leads to the higher fracture toughness and crack growth resistance curves. When compared with the standard SENB, the SENT specimen and the cracked pipe have a more similar fracture resistance behavior. The results present grounds for justification of usage of SENT specimens in fracture assessment of welding cracked pipes as an alternative to the traditional conservative SENB specimens.

Experimental Study on SCC Susceptibility of X60 Steel Using Full Pipe Sections in Near-Neutral pH Environment

2004 ◽  
Author(s):  
Bong Am Kim ◽  
Wenyue Zheng ◽  
G. Williams ◽  
M. Laronde ◽  
J. A. Gianetto ◽  
...  
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Loading Rate ◽  
Crack Depth ◽  
Metallographic Examination ◽  
Depth Measurement ◽  
Neutral Ph ◽  
Crack Tips ◽  
High Crack

Stress corrosion cracking (SCC) tests were performed using the pipe section buried in a clay type of soil with the pH adjusted to near-neutral range. Pipe specimens with various sizes of fatigue pre-cracks ahead of artifical notch tips on the outer surface were subjected to cyclic loading tests. Maximum level of hoop stress was 105% SMYS, and R-value (Ratio of minimum load to maximum load) was 0.5. Growth of cracks was observed from the fatigue crack tips. Fractographic and metallographic examination has confirmed the quasi-cleavage nature of the transgranular SCC that is typically observed in near-neutral pH SCC. Crack depth measurement using DCPD method revealed the relatively high crack growth rate up to 10−5 mm/s. Metallographic examinations showed the existence of many micro-cracks associated with MnS inclusions in the highly strained field ahead of the initial crack tips. The relatively high crack growth rate may be caused by MnS inclusions. The loading rate, dJ/dt, was calculated for each crack condition in order to correlate qualitatively the crack growth rate with the loading rate. J-integral was calculated through non-linear FEM analyses for semi-elliptical cracks based on the stress-strain relationships obtained from the tensile tests using the same X60 steel specimen. Linear relationship was then obtained between the crack growth rate and the loading rate, and therefore the possibility to predict crack growth rates for various loading condition in the field was demonstrated.

scholarly journals Segment tip geometry of sheet intrusions, I: Theory and numerical models for the role of tip shape in controlling propagation pathways

Volcanica ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 189-201
Author(s):  
Richard Walker ◽  
Tara Stephens ◽  
Catherine Greenfield ◽  
Simon Gill ◽  
David Healy ◽  
...  
Keyword(s):  
Numerical Models ◽  
Local Stress ◽  
Maximum Tensile Stress ◽  
Excess Pressure ◽  
Stress Concentrations ◽  
Length Scales ◽  
Element Simulation ◽  
Out Of Plane ◽  
Crack Tips

Inferences about sheet intrusion emplacement mechanisms have been built largely on field observations of intrusion tip zones: magmatic systems that did not grow beyond their observed state. Here we use finite element simulation of elliptical to superelliptical crack tips, representing observed natural sill segments, to show the effect of sill tip shape in controlling local stress concentrations, and the potential propagation pathways. Stress concentration magnitude and distribution is strongly affected by the position and magnitude of maximum tip curvature κmax. Elliptical tips concentrate stress in-plane with the sill, promoting coplanar growth. Superelliptical tips concentrate maximum tensile stress (σmax) and shear stress out-of-plane of the sill, which may promote non-coplanar growth, vertical thickening, or coplanar viscous indentation. We find that σmax =  Pe(1+ 2(√[aκmax]), where Pe is magma excess pressure and a is sill half length. At short length-scales, blunted tips locally generate large tensile stresses; at longer length-scales, elliptical-tipped sills become more efficient at concentrating stress than blunt sills.

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