Ductile Fracture Analysis Under Large Amplitude Cycles

2014 ◽  
Author(s):  
B. Tranchand ◽  
S. Chapuliot ◽  
V. Aubin ◽  
S. Marie ◽  
M. Bourgeois
Keyword(s):  
Crack Propagation ◽  
Fracture Energy ◽  
Ductile Fracture ◽  
Crack Closure ◽  
Large Amplitude ◽  
Crack Opening ◽  
Image Correlation ◽  
Potential Measurement ◽  
Loading Ratio

Demonstration of large components integrity under seismic loading is based up to now on monotonic tearing resistance curves. However, it is well known that cycles decrease the fracture resistance of the material, mainly according to the loading ratio. Most studies use monotonic methods to analyze reversible cyclic loading and the associated increase of crack propagation: Delta J-R curves are largely used. For monotonic loadings, Turner [1] proposed a decomposition of the rate of dissipated fracture energy. This decomposition led on the determination of an energetic criterion for ductile fracture [2]. This intrinsic criterion allows the fracture prediction on large components. This paper aims to propose an analysis of cyclic ductile fracture which should allow the determination of an energetic criterion under large amplitude cycles. For that purpose, compact tension specimens are taken from a carbon steel pipe (Tu42C) used in the secondary circuit of French PWR. A series of cyclic tearing tests are carried out under quasi-static loadings. The effects of loading ratio and incremental plastic displacement are quickly studied. Here, we present an energetic analysis which take into account the crack closure and crack opening. Indeed, displacement fields around the crack tips are measured with digital image correlation and linked with electric potential measurement. That allows an accurate determination of crack closure and crack opening and let a precise calculation of fracture energy possible. The energetic fracture criterion will be confirmed with crack propagation prediction on different geometry like CT specimen and a through-wall-cracked pipe under cyclic reversed loadings.

Fatigue Crack Propagation in Haynes 230: A Comparison between Single and Polycrystal Crack Closure Levels

2016 ◽  
Vol 258 ◽  
pp. 243-248 ◽  
Author(s):  
Stefano Beretta ◽  
Stefano Foletti ◽  
Silvio Rabbolini ◽  
Huseyin Sehitoglu
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Closure ◽  
Driving Forces ◽  
Crack Opening ◽  
Image Correlation ◽  
Accurate Estimation ◽  
Haynes 230 ◽  
Local Measurements ◽  
Plasticity Induced Crack Closure

An experimental campaign was developed to evaluate fatigue crack growth in Haynes 230. The effects of plasticity induced crack closure were investigated with Digital Image Correlation. In particular, crack opening levels were measured with the digital extensometer technique, which allowed the evaluation of crack flanks relative displacements. Experimental results were compared with a reference da/dn – ΔKeff curve and with the data of a previous study, which analyzed single crystal propagation. It was found that the adoption of crack closure local measurements provided an accurate estimation of crack propagation driving forces, since all the experimental points from single crystals and polycrystals collapse onto the da/dn – ΔKeff curve.

A Method to Identify the Crack Closure and Opening in Cyclic Tearing Tests on Fracture Mechanics Specimens

2014 ◽  
Author(s):  
B. Tranchand ◽  
V. Aubin ◽  
S. Marie
Keyword(s):  
Crack Closure ◽  
Kinematic Hardening ◽  
Crack Opening ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Image Correlation ◽  
Electric Signal ◽  
Specimen Thickness ◽  
Secondary Circuit ◽  
Potential Measurement

To measure crack propagation in compact tension specimen, many methods can be used. The electric drop potential measurement is one of them and allows the detection of crack initiation. In our case, CT specimens, which have been taken from a carbon steel pipe (Tu42C) used in the secondary circuit of French PWR, are employed for cyclic tearing test. The detection of crack closure and crack opening should provide information for energetic analysis. However, the electric signal is unusable due to the cyclic loading. Indeed, because of the clearance between the pin and the specimen, each direction loading change causes a discontinuity in the signal. The roughness of the lips surface or the crack closure during compression loading returns also an unusual signal. Moreover, local measurement is required and there is high strain level around the crack tips, so strain gages are not suitable. Thus, displacement field are measured with digital image correlation and a specific image acquisition is employed. These methods allow a direct measurement of strain fields on the surface of the specimen. Thereby an interpretation of the previous electric signal and the crack opening and closure detection is realizable. Then, F.E. simulation, with non-linear kinematic hardening and node release method, are performed. These simulations allow the check of crack opening and closure detection through the specimen thickness.

scholarly journals Experimental and Theoretical Determination of the Frost-Heave Cracking Law and the Crack Propagation Criterion of Slab Track with Water in the Crack

2019 ◽  
Vol 9 (21) ◽  
pp. 4592 ◽  
Author(s):  
Fengzhuang Tong ◽  
Liang Gao ◽  
Xiaopei Cai ◽  
Yanglong Zhong ◽  
Wenqiang Zhao ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Opening ◽  
Evaluation Criteria ◽  
Image Correlation ◽  
Frost Heave ◽  
External Temperature ◽  
Slab Track ◽  
Initiation And Propagation ◽  
Evolution Laws

Crack propagation produced by frost heave affects the durability of slab-track structures in high-humidity and cold regions in China. This work is intended to reveal the evolution laws of frost-heave crack propagation, establish evaluation criteria for crack propagation, and investigate factors involved in frost-heave crack propagation. Firstly, by preparing slab-track specimens with initial cracks, an experiment of frost-heave crack propagation was designed. The process of frost-heave crack propagation was carried out by means of digital image correlation (DIC) technology and acoustic emission (AE) technology, respectively. These experiments revealed the evolution laws of generalized strain and AE events’ location during crack initiation and propagation, respectively, and the key parameters of micro-crack initiation strain and unstable propagation strain were obtained. By using theoretical and experimental analysis, a double-strain criterion for frost-heave crack propagation was proposed. Finally, factors involved in frost-heave crack propagation were investigated. The results show that crack initiation can be reflected by the crack-tip strain. The average micro-crack initiation strain and unstable propagation strain were found to be 224 με and 243 με, respectively. Moreover, it was found that the frost-heave crack propagation was caused by an ice plug which formed at the crack opening. When the crack width is larger than 2.7 mm and the external temperature is lower than −6.6 °C, cracks propagate easily under the frost-heave force.

scholarly journals Dynamic crack propagation in weak snowpack layers: Insights from high-resolution, high-speed photography

2021 ◽  
Author(s):  
Bastian Bergfeld ◽  
Alec van Herwijnen ◽  
Benjamin Reuter ◽  
Grégoire Bobillier ◽  
Jürg Dual ◽  
...  
Keyword(s):  
High Resolution ◽  
Crack Propagation ◽  
Fracture Energy ◽  
High Speed ◽  
Image Correlation ◽  
Crack Speed ◽  
Specific Fracture Energy ◽  
Weak Layer ◽  
Specific Fracture ◽  
Insight Into

Abstract. To assess snow avalanche release probability, information on failure initiation and crack propagation in weak snowpack layers underlying cohesive slab layers are required. With the introduction of the Propagation Saw Test (PST) in the mid-2000s, various studies used particle tracking analysis of high-speed video recordings of PST experiments to gain insight into crack propagation processes, including slab bending, weak layer collapse, crack propagation speed and the frictional behavior after weak layer fracture. However, the resolution of the videos and the methodology used did not allow insight into dynamic processes such as the evolution of crack speed within a PST or the touchdown distance, which is the length from the crack tip to the trailing point where the slab sits on the crushed weak layer at rest again. Therefore, to study the dynamics of crack propagation we recorded PST experiments using a powerful portable high-speed camera with a horizontal resolution of 1280 pixels at rates up to 20,000 frames per second. By applying a high-density speckling pattern on the entire PST column, we then used digital image correlation (DIC) to derive high-resolution displacement and strain fields in the slab, weak layer, and substrate. The high frame rates allowed time derivatives to obtain velocity and acceleration fields. On the one hand, we demonstrate the versatile capabilities and accuracy of the DIC method by showing three PST experiments resulting in slab fracture, crack arrest and full propagation. On the other hand, we present a methodology to determine relevant characteristics of crack propagation: the crack speed and touchdown distance within a PST, and the specific fracture energy of the weak layer. To estimate the effective elastic modulus of the slab and weak layer as well as the weak layer specific fracture energy we used a recently proposed mechanical model. A comparison to already established methods showed good agreement. Furthermore, our methodology also provides insight into the three different propagation results found with the PST and reveals intricate dynamics that are otherwise not accessible.

Determination of CTOD Resistance Curves in SENT Specimens With a Tilted Notch

2014 ◽  
Author(s):  
Koen Van Minnebruggen ◽  
Matthias Verstraete ◽  
Rudi Denys ◽  
Philippe Thibaux ◽  
Wim De Waele
Keyword(s):  
Crack Opening ◽  
Potential Drop ◽  
Element Model ◽  
Image Correlation ◽  
Pure Mode ◽  
Opening Displacement ◽  
Thermo Electric ◽  
Seam Weld ◽  
Tearing Resistance

The Single Edge Notched Tension (SENT) specimen is a common tool for the determination of tearing resistance in pipeline steels and welds. However, it assumes pure mode I crack tip loading, which is unrepresentative for the evaluation of spiral seam weld flaws. To this purpose, the authors have performed SENT tests using specimens with a tilted notch. This paper evaluates experimental techniques to obtain the tearing resistance of such specimens. Mixed-mode crack opening displacement and ductile tearing are successfully measured using digital image correlation and direct current potential drop, respectively. The latter technique involves a calibration on the basis of a thermo-electric finite element model. Tearing resistance tends to increase with increasing notch tilt angle. Based on the limited number of tests performed, tilted notch SENT testing appears to be a promising tool for the assessment of spiral seam weld flaws.

scholarly journals New experimental techniques for dynamic crack localization

2009 ◽  
pp. 255-283
Author(s):  
David Grégoire ◽  
Hubert Maigre ◽  
Fabrice Morestin
Keyword(s):  
Crack Propagation ◽  
Crack Tip ◽  
Image Correlation ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Displacement Sensors ◽  
Optical Displacement ◽  
Propagation Parameters ◽  
Tip Position

The determination of relevant constitutive crack propagation laws under dynamic loading is a rather challenging operation. In dynamic impact cases, the variations of propagation parameters and exact crack positions are difficult to control. This paper focuses on different techniques for measuring accurate crack tip position histories in dynamic crack propagation experiments. Two different methods are considered: very accurate crack tip localization by optical displacement sensors is first described for transparent materials; then, an automatic method based on digital image correlation is presented for crack localization in all brittle materials whatever their opacity.

Fracture Characterization of Human Cortical Bone Under Mode I Loading

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Filipe Silva ◽  
Marcelo de Moura ◽  
Nuno Dourado ◽  
José Xavier ◽  
Fábio Pereira ◽  
...  
Keyword(s):  
Fracture Energy ◽  
Cortical Bone ◽  
Crack Opening ◽  
Image Correlation ◽  
Cohesive Zone Modeling ◽  
Mode I ◽  
Pure Mode ◽  
Cohesive Law ◽  
Human Cortical Bone ◽  
Mode I Loading

A miniaturized version of the double cantilever beam (DCB) test is used to determine the fracture energy in human cortical bone under pure mode I loading. An equivalent crack length based data-reduction scheme is used with remarkable advantages relative to classical methods. Digital image correlation (DIC) technique is employed to determine crack opening displacement at the crack tip being correlated with the evolution of fracture energy. A method is presented to obtain the cohesive law (trapezoidal bilinear softening) mimicking the mechanical behavior observed in bone. Cohesive zone modeling (CZM) (finite-element method) was performed to validate the procedure showing excellent agreement.

On the Gasdynamics of Running Ductile Fracture in a Pressurized Line Pipe

1978 ◽  
Vol 100 (1) ◽  
pp. 13-17 ◽  
Author(s):  
D. M. Parks ◽  
L. B. Freund
Keyword(s):  
Crack Propagation ◽  
Ductile Fracture ◽  
Driving Force ◽  
Crack Opening ◽  
Two Dimensional ◽  
Line Pipe ◽  
New Model ◽  
Large Crack ◽  
Two Dimensional Flow ◽  
Axial Crack

Developments in the modeling of the gasdynamics associated with running ductile fracture in pressurised line pipe are reviewed and critically examined. It is argued that existing models of gas escape through a flaring axial crack in a pipe may not be generally applicable. A new model of gas escape, based on two-dimensional flow and directed toward large crack opening situations, is presented, and results obtained with this model compare favorably with experiments. Implications of the present results concerning the driving force for crack propagation are discussed.

Information and estimation in image processing

1987 ◽  
Vol 45 ◽  
pp. 14-17
Author(s):  
B. Roy Frieden
Keyword(s):  
Image Processing ◽  
Optical System ◽  
Large Amplitude ◽  
Communication Theory ◽  
Image Data ◽  
Direct Approach ◽  
Ill Posed

Despite the skill and determination of electro-optical system designers, the images acquired using their best designs often suffer from blur and noise. The aim of an “image enhancer” such as myself is to improve these poor images, usually by digital means, such that they better resemble the true, “optical object,” input to the system. This problem is notoriously “ill-posed,” i.e. any direct approach at inversion of the image data suffers strongly from the presence of even a small amount of noise in the data. In fact, the fluctuations engendered in neighboring output values tend to be strongly negative-correlated, so that the output spatially oscillates up and down, with large amplitude, about the true object. What can be done about this situation? As we shall see, various concepts taken from statistical communication theory have proven to be of real use in attacking this problem. We offer below a brief summary of these concepts.

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