Comparison of Potential Drop and Unloading Compliance Methods in Determining Ductile Crack Extension

2008 ◽  
pp. 363-363-12
Author(s):  
K Wallin ◽  
T Saario ◽  
P Auerkari ◽  
H Saarelma ◽  
K Torronen
Keyword(s):  
Crack Extension ◽  
Potential Drop ◽  
Ductile Crack ◽  
Unloading Compliance

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.

Evaluation and interpretation of ductile crack extension in SENT specimens using unloading compliance technique

2014 ◽  
Vol 115 ◽  
pp. 190-203 ◽  
Author(s):  
M.A. Verstraete ◽  
S. Hertelé ◽  
R.M. Denys ◽  
K. Van Minnebruggen ◽  
W. De Waele
Keyword(s):  
Crack Extension ◽  
Ductile Crack ◽  
Unloading Compliance

Ductile Crack Extension Analysis for X80 Bending Deformation Using Damage-Based Model

2014 ◽  
Author(s):  
Satoshi Igi ◽  
Mitsuru Ohata ◽  
Takahiro Sakimoto ◽  
Kenji Oi ◽  
Joe Kondo
Keyword(s):  
Plastic Strain ◽  
Simulation Model ◽  
Crack Growth ◽  
Crack Extension ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Ductile Crack Growth ◽  
Notch Tip

This paper presents experimental and analytical results focusing on the strain limit of X80 linepipe. Ductile crack growth behavior from a girth weld notch is simulated by FE analysis based on a proposed damage model and is compared with the experimental results. The simulation model for ductile crack growth accompanied by penetration through the wall thickness consists of two criteria. One is a criterion for ductile crack initiation from the notch-tip, which is described by the plastic strain at the notch tip, because the onset of ductile cracking can be expressed by constant plastic strain independent of the shape and size of the components and the loading mode. The other is a damage-based criterion for simulating ductile crack extension associated with damage evolution influenced by plastic strain in accordance with the stress triaxiality ahead of the extending crack tip. The proposed simulation model is applicable to prediction of ductile crack growth behaviors from a circumferentially-notched girth welded pipe with high internal pressure, which is subjected to tensile loading or bending (post-buckling) deformation.

Improved Compliance Solutions for C(T), SE(B) and Clamped SE(T) Specimens Including Side-Grooves, Varying Thicknesses and 3-D Effects

2014 ◽  
Author(s):  
Gustavo Henrique B. Donato ◽  
Felipe Cavalheiro Moreira
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Potential Drop ◽  
Crack Size ◽  
Growth Conditions ◽  
Size Estimation ◽  
Unloading Compliance ◽  
Integrity Assessments ◽  
Elastic Unloading

Fracture toughness and Fatigue Crack Growth (FCG) experimental data represent the basis for accurate designs and integrity assessments of components containing crack-like defects. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. ΔK or ΔJ) assumed paramount relevance since characterize, respectively, ductile fracture and cyclic crack growth conditions. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen’s thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain - modulus vary between E (plane stress) and E/(1-ν2) (plane strain), revealing effects of thickness and 3-D configurations; ii) furthermore, side-grooves affect specimen’s stiffness, leading to an “effective thickness”. Previous results from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging clamped SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D, thickness and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W=0.1 and a/W=0.7 and varying thicknesses (W/B = 4, W/B = 2 and W/B = 1). Side-grooves of 5%, 10% and 20% are also considered. The results include compliance solutions incorporating all aforementioned effects to provide accurate crack size estimation during laboratory fracture and FCG testing. All proposals revealed reduced deviations if compared to existing solutions.

scholarly journals Evaluation of ductile tearing for API-5L X70 pipeline grade steel using SENT specimens

2015 ◽  
Vol 6 (3) ◽  
pp. 8
Author(s):  
Nicholas Ohms ◽  
Diego Belato Rosado ◽  
Wim De Waele
Keyword(s):  
Crack Growth ◽  
Crack Extension ◽  
Crack Growth Resistance ◽  
Fracture Surfaces ◽  
Edge Notch ◽  
Resistance Curves ◽  
Unloading Compliance ◽  
Inner Diameter ◽  
Tearing Resistance ◽  
Hardness Map

Pipelines in harsh environments may be subjected to large deformations. Classic stress-based design needs to be complemented with strain-based design. An important parameter in the design is the crack growth resistance. SENT testing (Single Edge Notch Tension) allows to determine the so-called material’s tearing resistance curve. Very recently the first standard on SENT testing, BS 8571:2014, has been published. SENT testing is however still subject to extensive research and different approaches with respect to eg. notch placement, crack extension measurement and analysis exist. In this paper two methods for calculating crack extension based on the unloading compliance procedure are used and compared, proving that they show little difference. This is performed on an API-5L X70 steel grade and this for different configurations, namely an inner diameter notch and a through thickness notch. The results showed little difference between the different configurations, although the inner diameter showed higher crack growth resistance. Furthermore, the results are compared to visual observations of the fracture surfaces and a hardness map. The fracture surfaces corresponded to the obtained resistance curves. However, no real correlation between the hardness map and the other results could be seen.

The Influence of Creep Strain on Crack Length Measurements Using the Potential Drop

2015 ◽  
Author(s):  
K. M. Tarnowski ◽  
C. M. Davies ◽  
K. M. Nikbin ◽  
D. W. Dean
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Material Properties ◽  
Crack Extension ◽  
Electrical Potential ◽  
Creep Crack Growth ◽  
Potential Drop ◽  
Fe Model ◽  
Creep Properties ◽  
Length Measurements

One of the most common methods for estimating crack extension in the laboratory is electrical potential drop (PD). A key limitation of this technique is that it is sensitive to strains at the crack tip as well as crack extension. When producing J-R curves the onset of crack growth may be identified from a point of inflection on a plot of PD vs. CMOD. For creep crack growth (CCG) tests however, the effects of strain are often ignored. This paper investigates whether a similar method may be applied to CCG testing. A single CCG test was performed on type 316H stainless steel and a point of inflection, similar to that observed during J-R curve testing was identified. A finite element (FE) based approach was used to investigate this phenomenon further. A 3D sequentially-coupled structural-electrical FE model was used to reproduce the experimental PD vs. CMOD plot up to the point of inflection. The model was capable of predicting the general relationship between strain and PD. It predicted the magnitude of the change in PD to within 30%. A simplified 2D FE model was then used to perform a parametric study to investigate whether a similar trend may be expected for a range of materials. Power law tensile and creep properties were investigated with stress exponents of 1, 3 and 10. The results confirm that a point of inflection should be observable for the range of material properties considered.

The Development of a Surface Crack in a Thick Vessel Under Ductile Tearing

2009 ◽  
Author(s):  
Osama Terfas ◽  
Bostjan Bezensek
Keyword(s):  
Crack Extension ◽  
Driving Forces ◽  
Ductile Crack ◽  
Ductile Tearing ◽  
Surface Flaws ◽  
Resistance Curves ◽  
The Mean ◽  
Surface Breaking Crack ◽  
Tearing Resistance ◽  
Leak Before Break

The development of the shape and size of a flaw in a pressure vessel is important in fitness-for-service evaluations such as leak-before-break. In this work finite element modelling is used to evaluate the mean stresses and the J-integral around a front of a surface-breaking flaw. These results show non-uniform constraint levels and crack driving forces around the crack front at large deformation levels, which contrast those at low deformation levels. A new procedure is developed to estimate the amount of ductile crack extension around a surface-breaking crack on the basis of ductile tearing resistance curves of deep and shallow cracked fracture mechanics samples. The procedure is applied to surface flaws to simulate ductile crack extension under ductile tearing and show the evolution of the initial flaw shape. Results show that both, initially semi-circular and initially semi-elliptical flaws develop towards the same shape in bending.

scholarly journals Development of PFM Code with a Function of Ductile Crack Extension Analysis.

2003 ◽  
Vol 69 (678) ◽  
pp. 463-469 ◽  
Author(s):  
Yinsheng LI ◽  
Daisuke KATO ◽  
Katsuyuki SHIBATA ◽  
Kunio ONIZAWA
Keyword(s):  
Crack Extension ◽  
Ductile Crack ◽  
Extension Analysis
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