Reduced-thickness CVN testing to represent slant failure of pipelines

2013 ◽  
Vol 4 (1) ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Philippe Thibaux ◽  
Patrick Goes
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Propagation Speed ◽  
High Strength ◽  
Dissipated Energy ◽  
Specimen Thickness ◽  
Absorbed Energy ◽  
Element Analysis ◽  
The Difference ◽  
Energy Dissipated

To avoid longitudinal ductile crack propagation along a gas pipeline, the Batelle Two Curve method is used during pipeline design. This method states that a running crack will be arrested if the gas decompression velocity exceeds the crack propagation speed at the internal gas pressure. The crack propagation curve is scaled by impact energy values obtained through Charpy V-Notch (CVN) testing. However, for high-strength steel grades this scaling leads to unconservative predictions, because the experiment does not sufficiently represent the pipeline failure mode. The CVN specimen exhibits mainly mode I failure, without significant shear lips, while real failure is a combined mode often described as slant failure. In the present study, instrumented CVN tests are carried out on samples with different thickness reduction levels. To get a better insight in the crack initiation and propagation behaviour, the CVN test is simulated by finite element analysis. The dissipated energy and resulting fracture surfaces can be successfully represented. It is observed that slant failure is promoted by reducing the specimen thickness. In addition, the specific absorbed energy is decreased. However, most of the difference of absorbed energy is in crack initiation. This means that the fraction of the total energy dissipated in crack propagation is increased for reduced thickness specimens, making it a possible tool to assess the resistance of a material to crack propagation, provided that brittle fracture is avoided.

Modelling of Slant Failure Using Small Size Specimen

2012 ◽  
Author(s):  
Philippe Thibaux ◽  
Jeroen Van Wittenberghe
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Charpy Specimen ◽  
The Finite Element Method ◽  
Ductile Crack ◽  
Small Size Specimen ◽  
The Difference ◽  
Energy Dissipated ◽  
Small Shear ◽  
Combined Mode

The instability of a pipeline crack eventually leads to brittle or ductile crack propagation. The resistance to ductile crack propagation is assessed by the energy dissipated in the CVN test. However the Charpy specimen exhibits mainly mode I failure, with no small shear lips, while real failure is a combined mode often described as slant failure. In the present investigation, instrumented Charpy tests with nominal and reduced thickness down to 2.5 mm are carried out. Instrumented Battelle drop weight tear tests where also performed with nominal and reduced thickness, in order to vary the ligament versus thickness ratio. The results of the Charpy tests are simulated by the finite element method. The results are then discussed in terms of energy dissipated during crack initiation and crack propagation. It is shown that by reducing the size of the Charpy specimen, slant failure is promoted, which results in a decrease of the specific energy absorbed. However, most of the difference of absorbed energy is in the crack initiation mode, and only marginally in crack propagation. Consequently, the fraction of the total energy dissipated in crack propagation is increased by reducing the sample thickness, making it a possible tool to assess the resistance of a material to crack propagation, provided that brittle fracture is avoided and no separation is present.

scholarly journals Experimental and Numerical Study of Fracture Behavior of Rock-Like Material Specimens with Single Pre-Set Joint under Dynamic Loading

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2690
Author(s):  
Bo Pan ◽  
Xuguang Wang ◽  
Zhenyang Xu ◽  
Lianjun Guo ◽  
Xuesong Wang
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Joint Angle ◽  
Simulation Software ◽  
Dissipated Energy ◽  
Energy Structure ◽  
Joint Angles ◽  
Crack Penetration ◽  
Before And After ◽  
The Impact

The Split Hopkinson Pressure Bar (SHPB) is an apparatus for testing the dynamic stress-strain response of the cement mortar specimen with pre-set joints at different angles to explore the influence of joint attitudes of underground rock engineering on the failure characteristics of rock mass structure. The nuclear magnetic resonance (NMR) has also been used to measure the pore distribution and internal cracks of the specimen before and after the testing. In combination with numerical analysis, the paper systematically discusses the influence of joint angles on the failure mode of rock-like materials from three aspects of energy dissipation, microscopic damage, and stress field characteristics. The result indicates that the impact energy structure of the SHPB is greatly affected by the pre-set joint angle of the specimen. With the joint angle increasing, the proportion of reflected energy moves in fluctuation, while the ratio of transmitted energy to dissipated energy varies from one to the other. NMR analysis reveals the structural variation of the pores in those cement specimens before and after the impact. Crack propagation direction is correlated with pre-set joint angles of the specimens. With the increase of the pre-set joint angles, the crack initiation angle decreases gradually. When the joint angles are around 30°–75°, the specimens develop obvious cracks. The crushing process of the specimens is simulated by LS-DYNA software. It is concluded that the stresses at the crack initiation time are concentrated between 20 and 40 MPa. The instantaneous stress curve first increases and then decreases with crack propagation, peaking at different times under various joint angles; but most of them occur when the crack penetration ratio reaches 80–90%. With the increment of joint angles in specimens through the simulation software, the changing trend of peak stress is consistent with the test results.

Crack Propagation Prediction Using Haensel Damage Model

2012 ◽  
Author(s):  
Piotr Bednarz ◽  
Jaroslaw Szwedowicz
Keyword(s):  
Cyclic Loading ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Damage Model ◽  
Lifetime Prediction ◽  
Dissipated Energy ◽  
Mathematical Approach ◽  
Loading Conditions ◽  
Stored Energy ◽  
Tensile Stresses

The Haensel damage model correlates lifetime of a component until crack initiation to the dissipated and stored energy in the material during cyclic loading. The crack initiation is influenced by mean stresses. The Haensel damage model considers the mean stress effect by including compressive and tensile stresses in calculations of elastic strain energy during cyclic loading conditions. The goal of the paper is to extend the above model to predict crack propagation under large cyclic plasticity and non-proportional loading conditions. After voids initiation onset of necking, voids growth and linking takes place among them. During this process a mesocrack is created. This stage of fracture involves the same amount of released energy for new crack surface creation as dissipated energy for mesocrack initiation. The amount of dissipated and stored energy is related to the process zone size and to the number of cycles. Ilyushin’s postulate is used to calculate the amount of dissipated energy. In order to consider a contribution of tensile stresses only during loading to crack propagation, tensile/compressive split is performed for the stress tensor. One of the key drivers of this paper is to provide a straightforward engineering approach, which does not require explicit modelling of cracks. The proposed mathematical approach accounts for redistribution of stresses, strains and energy during crack propagation. This allows to approximate the observed effect of distribution of dissipated energy on the front of a crack tip. The developed approach is validated through FE (Finite Element) simulations of the Dowling and Begley experiment. The Haensel lifetime prediction of Dowling’s experiment is in good agreement with the experimental data and the explicit FE results. Finally, the proposed mathematical approach simplifies significantly the engineering effort for Nonlinear Fracture Mechanics lifetime prediction by avoiding the requirement to simulate real crack propagation using node base release methods, XFEM or remeshing procedures.

scholarly journals The Multi-Breakage Phenomenon in Air Bending Process

2014 ◽  
Vol 611-612 ◽  
pp. 1047-1053 ◽  
Author(s):  
Vitalii Vorkov ◽  
Richard Aerens ◽  
Dirk Vandepitte ◽  
Joost R. Duflou
Keyword(s):  
Finite Element ◽  
High Strength ◽  
Large Radius ◽  
Element Analysis ◽  
Bending Force ◽  
Bending Process ◽  
The Difference ◽  
The Moment ◽  
Force Calculation ◽  
Three Phases

In this work, the multi-breakage effect has been studied by means of an experimental campaign and finite element analysis. We suggest that large radius bending (XL-bending) consists of three phases that are distinguishable according to the type of contact of the plate with the tool: 1-point, surface and 2-points. In the experimental investigation the high-strength steel Weldox 1300 and a 40 mm radius punch were used. The authors created a camera setup to film the multi-breakage effect. Additionally, finite-element calculations were performed to confirm the hypothesis of the three phases of the bending process. For the springback and the bending force evaluation, the difference in the moment distribution for each phase has been calculated in the case of a beam. It shows that the multi-breakage effect must be taken into account to obtain a good accuracy for the springback and the bending force calculation.

scholarly journals Study on the Fracture Behavior of Cracks Emanating from Tunnel Spandrel under Blasting Loads by Using TMCSC Specimens

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Bang Liu ◽  
Zheming Zhu ◽  
Ruifeng Liu ◽  
Lei Zhou ◽  
Duanying Wan
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Fracture Behavior ◽  
Propagation Speed ◽  
Propagation Path ◽  
Propagation Time ◽  
Dynamic Stress Intensity Factors ◽  
Inclination Angles ◽  
Crack Propagation Speed ◽  
Radial Cracks

Radial cracks may exist around tunnel edge, and these cracks may propagate and weaken tunnel stability under nearby blasting operations. In order to study the blast-induced fracture behavior of radial cracks emanating from a tunnel spandrel, a tunnel model containing a spandrel crack (TMCSC) with different inclination angles was proposed in this paper. Crack propagation gauges (CPGs) and strain gauges were used in the experiments to measure crack initiation moment and propagation time. Finite difference models were established by using AUTODYN code to simulate crack propagation behavior and propagation path. ABAQUS code was used to calculate dynamic stress intensity factors (SIFs). The results show that (1) crack inclination angles affect crack initiation angles and crack propagation lengths significantly; (2) critical SIFs of both mode I and mode II decrease gradually with the increase of the crack propagation speed; (3) the dynamic energy release rates vary during crack propagation; and (4) there are “crack arrest points” on the crack propagation paths in which the crack propagation speed is very small.

Cleavage Fracture of Ultra-High-Strength Steels. Microscopic Observations. Numerical Analysis. Local Fracture Criterion

2014 ◽  
Vol 598 ◽  
pp. 168-177 ◽  
Author(s):  
Andrzej Neimitz ◽  
Ihor Dzioba ◽  
Urszula Janus
Keyword(s):  
Material Property ◽  
Cleavage Fracture ◽  
High Strength Steels ◽  
High Strength ◽  
Critical Value ◽  
Experimental Program ◽  
Fracture Mechanisms ◽  
Specimen Thickness ◽  
Element Analysis ◽  
Ultra High Strength Steels

In the paper the fracture mechanisms in ultra-high-strength steel are examined. However, the emphasis is on cleavage fracture, which was observed in the whole temperature range tested. The extent of cleavage depends on the specimen thickness and temperature. The experimental program consisted of tensile and fracture tests and was followed by scanning microscope observations of the fracture surfaces. Then, a full 3D elastic-plastic finite element analysis was carried out assuming finite strains. The numerical results support the postulate that the onset of cleavage jump is observed when the maximum opening stresses become higher than the critical value (the material property at a given temperature) over a distance greater than the critical value (material property independent of temperature). A discussion of so-called 3D stress parameters is presented.

Effect of Specimen Thickness on Fatigue Crack Propagation in High Strength Steels

1982 ◽  
Vol 25 (206) ◽  
pp. 1195-1201 ◽  
Author(s):  
Keizo FUJITANI ◽  
Tatsuo SAKAI ◽  
Akiyoshi NAKAGAWA ◽  
Tsuneshichi TANAKA
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
High Strength Steels ◽  
High Strength ◽  
Specimen Thickness

scholarly journals Autofrettage of component-like ultra high Strength Steel Specimens with intersecting Holes

2021 ◽  
Vol 349 ◽  
pp. 04004
Author(s):  
Carl Fällgren ◽  
Thomas Beier ◽  
Michael Vormwald ◽  
Andreas Kleemann
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Stress Distribution ◽  
Crack Initiation ◽  
Crack Propagation ◽  
High Strength Steel ◽  
High Strength ◽  
Crack Arrest ◽  
Residual Stress Distribution ◽  
Ultra High Strength Steel

This work is primarily concerned with the fatigue life of high-pressure-bearing components with intersecting holes, typically used in Diesel engine fuel injection systems. The investigation focuses on specimens with intersecting holes that have undergone the process of Autofrettage (single mechanical overload), which is typically used to extend the fatigue life of components loaded by cyclic internal pressure. The resulting residual stress distribution thus influences the fatigue failure and especially the crack propagation behaviour of the components. In previous works, results showed that besides crack initiation, crack arrest behaviour has to be taken into account when calculating fatigue lives of autofrettaged specimens as the endurance limit is otherwise underestimated. In order to achieve reliable results, material testing with samples made of the ultra high strength steel W360 was performed. The resulting test data were used to simulate the Autofrettage process with finite-element analysis. Calculated residual stress distributions were used to determine at which levels of subsequent cyclic loading crack initiation would occur. For predicted crack initiation, the simulated residual stress distribution was used to investigate the crack propagation behaviour with fracture mechanics based approaches of different complexity in order to identify possible crack arrest or crack propagation. Calculated results were compared to experimental test data from component-like specimens. The comparison showed that the fracture mechanics based approaches are capable of describing the crack arrest and propagation behaviour reliably.

scholarly journals Effect of Bainitic Microstructure on Low-Temperature Toughness of High-Strength API Pipeline Steels

2020 ◽  
Vol 58 (5) ◽  
pp. 293-303
Author(s):  
Seung-Wan Lee ◽  
Sang-In Lee ◽  
Byoungchul Hwang
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Crack Initiation ◽  
High Strength ◽  
Processing Conditions ◽  
Absorbed Energy ◽  
Pipeline Steels ◽  
Bainitic Microstructure ◽  
Effective Grain Size ◽  
Low Temperature Toughness

In this study the correlation between bainitic microstructure and the low-temperature toughness of high-strength API pipeline steels was discussed in terms of crack initiation and propagation in the microstructure. Three types of API pipeline steels with different bainitic microstructures were fabricated using varying alloying elements and thermo-mechanical processing conditions, and then their microstructure was characterized by optical and scanning electron microscopy, and electron backscatter diffraction (EBSD). In particular, the effective grain size and microstructure fraction of the steels were quantitatively measured by EBSD analysis. Although all the steels were composed of polygonal ferrite (PF), and complex bainitic microstructures such as acicular ferrite (AF), granular bainite (GB), and bainitic ferrite (BF), they had different effective grain sizes and microstructure fraction, depending on the alloying elements and thermomechanical processing conditions. Charpy impact test results showed that when the martensite-austenite constituent fraction was lowest, it resulted in higher upper-shelf energy, and absorbed energy at room temperature due to the decrease in crack initiation. In contrast, excellent low-temperature toughness, such as lower ductile-brittle transition temperature and higher absorbed energy at low temperatures, could be achieved with a bainitic microstructure with fine effective grain size and high fraction of high-angle grain boundaries, which act as obstacles to prevent cleavage crack propagation.

A Simplified Method for Estimating the Amount of Energy Dissipated by Flexure-Dominated Reinforced Concrete Members for Moderate Cyclic Deformations

2006 ◽  
Vol 22 (2) ◽  
pp. 459-490 ◽  
Author(s):  
Honggun Park ◽  
Taesung Eom
Keyword(s):  
Reinforced Concrete ◽  
Compressive Force ◽  
Cyclic Behavior ◽  
Dissipated Energy ◽  
Structural Walls ◽  
Element Analysis ◽  
Axial Compressive Force ◽  
Concrete Members ◽  
Simplified Method ◽  
Energy Dissipated

In advanced earthquake analysis/design methods, the cyclic behavior of reinforced concrete (RC) members, which is characterized by strength, deformability, and the amount of dissipated energy, must be estimated with reasonable precision. However, presently, the amount of dissipated energy is estimated by either empirical equations, which are not sufficiently accurate, or experiments and sophisticated numerical analysis, which are difficult to use in practice. In the present study, nonlinear finite element analysis was performed to investigate the behavioral characteristics of flexure-dominated RC members subject to moderate plastic displacements. The results showed that flexural pinching can occur due to the effects of axial compressive force and asymmetrical rebar arrangement. However, axial force has little effect on the energy dissipation. The arrangement and ratio of reinforcement have substantial effects. Based on the findings, a simplified method to estimate the energy dissipated by flexure-dominated members was developed, and was verified by comparing its results with those of existing experiments on beams, columns, and structural walls.

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