Ductile Fracture Characterization of an X70 Steel: Re-Interpretation of Classical Tests Using the Finite Element Technique

2008 ◽  
Author(s):  
Philippe Thibaux ◽  
Se´bastien Mu¨ller ◽  
Benoit Tanguy ◽  
Filip Van Den Abeele
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Pipeline Steel ◽  
Damage Model ◽  
Base Material ◽  
Steel Production ◽  
Crack Arrest ◽  
Finite Element Simulations ◽  
Charpy Test ◽  
The Impact

The crack arrest capacity of a linepipe is one of the most important material parameter for such components. In current design codes, it is expressed as the energy absorbed by a CVN impact test. This prescribed impact energy for a given pipeline is typically between 50 and 120J, depending on the grade of the material, the pressure and the dimensions of the pipe. The continuous improvement of steel production has lead to the situation that the impact values achieved in standard pipeline steel production are much larger than 200J for the base material. The question of the significance of these high impact energies can be raised, particularly considering that no correlation has been found between CVN values and crack arrest properties of very high strength materials (X100–X120). In this investigation, instrumented Charpy tests and notched tensile tests were performed on an X70 material. The same tests were also simulated using the finite element method and the Gurson-Tvergaard-Needleman damage model. The combination of supplementary experimental information coming from the instrumentation of the Charpy test and finite element simulations delivers a different insight about the test. It is observed that the crack does not break the sample in 2 parts in ductile mode. After 6–7mm of propagation, the crack deviates and stops. The propagation stops when the crack meets the part of the sample becoming wider due to bending. Finite element simulations proved that it results in a quasi constant force during a displacement of the hammer of almost 10mm. The consequence is that more than 25% of the energy is dissipated in a different fracture mode at the end of the test. Finite element simulations proved also that damage is already occurring at the maximum of the load, but that damage has almost no influence on the load for two-thirds of the displacement at the maximum. In the case of the investigated steel, it means that more than 27J, as often mentioned in standards for avoidance of brittle failure, are dissipated by plastic bending before the initiation of the crack. From the findings of this study, one can conclude that the results of the Charpy test are very sensitive to crack initiation and that only a limited part of the test is meaningful to describe crack propagation. Therefore, it is questionable if the Charpy test is adapted to predict the crack arrest capacity of steels with high crack initiation energy.

Finite element simulation of dynamic brittle fracture in pipeline steel: A XFEM-based cohesive zone approach

2016 ◽  
Vol 232 (5) ◽  
pp. 357-370
Author(s):  
Reza Hojjati-Talemi ◽  
Steven Cooreman ◽  
Dennis Van Hoecke
Keyword(s):  
Finite Element ◽  
Brittle Fracture ◽  
Cohesive Zone ◽  
Pipeline Steel ◽  
Temperature Drop ◽  
Charpy Impact ◽  
Large Temperature ◽  
Charpy Test ◽  
Line Pipe ◽  
The Impact

Leaking in a CO2 pipeline could escalate to sudden crack propagation, due to a large temperature drop. The resulting drop in fracture toughness together with the pressure stresses at the defect plane leads to pipeline brittle fracture. The main objective of this study is to monitor and predict brittle fracture behaviour of API X70 pipeline steel by means of experimental and numerical approaches, respectively. Dynamic fracture properties of CO2 line pipe steels are generally assessed using the Charpy impact test. To this end, Charpy V-notch tests are performed at different temperatures in order to study the resistance of materials subjected to impact loading conditions. The Charpy test provides valuable indications on the impact properties of materials. Using the experimental results the ductile to brittle transition temperature curve is presented. The extended finite element method based cohesive zone approach is introduced to model the brittle fracture at low temperature. After validation of the developed model against experimental observation significant results from the simulation are graphically presented and discussed.

Estimation of Slant Tearing Energy for High-Grade Pipeline Steel From Instrumented Charpy Test Data and its Transferability to Large Structures

2006 ◽  
Author(s):  
Sayyed H. Hashemi ◽  
Ian C. Howard ◽  
John R. Yates ◽  
Robert M. Andrews ◽  
Alan M. Edwards
Keyword(s):  
Crack Initiation ◽  
Fracture Energy ◽  
Pipeline Steel ◽  
Crack Arrest ◽  
Correction Factors ◽  
Charpy Test ◽  
Pipeline Steels ◽  
Fracture Models ◽  
Slant Fracture ◽  
Tearing Energy

For several decades, the Charpy upper shelf energy has been used as a fracture controlling parameter to estimate the crack arrest/propagation performance of gas transportation pipeline steels. However, significant discrepancies have been observed between the results of full-scale burst experiments on modern pipeline steels and those predicted by Charpy-based fracture models. This indicates that fracture models calibrated in the past on lower-grade pipeline steels (Charpy toughness below about 100J) cannot be extrapolated beyond their calibration range to assess the fracture behaviour of higher-strength high-toughness steels. One reason for this is the high level of energy often required for crack initiation in these steels. Accordingly, in the short term different correction factors ranging from 1.4 to 2 have been proposed to refine these fracture prediction models. The use of alternative failure parameters like CTOA is currently under review. In this paper a novel experimental technique is given to apportion the upper shelf Charpy fracture energy into its different components, i.e. crack initiation energy and flat and slant tearing energy. The experimental data from instrumented Charpy tests on standard impact specimens made from an X100 grade pipeline steel is used to estimate crack initiation and propagation energy. The areas associated with flat tearing in the centre and slant shearing at the edges of the fracture surface of Charpy test specimens are estimated optically using a fine measurement grid with 0.5 mm spacing. The energy required for generating the flat and slant fracture areas is calculated by the use of associated multipliers, i.e. the specific flat and slant fracture energy (in terms of J/mm2). These are measured separately using flat and slant crack growth data from fracture tests on standard C(T) and modified DCB like specimens. The results showed that the Charpy energy from a test is dominated by non-crack propagation energies. Around 36% of the measured impact energy appeared to be associated with flat and slant tearing processes. As the latter is the important failure micro-mechanism in pipeline steel only that part of the overall Charpy shelf energy which is associated with slant shearing might be used to evaluate the crack growth resistance of modern steels. This suggests the possible use of correction factors for high toughness pipeline steels of the order of 1.7 to transfer the slant fracture energy measured on small-scale specimens to the real structures for predicting their crack arrest/propagation behaviour. The correction factor proposed here from the laboratory test programme agrees with those obtained from costly full-thickness burst experiments on similar class of pipeline steel.

A Study of the Importance of Three Key Parameters on the Separation Modes of Adhering Microcontacts

2007 ◽  
Author(s):  
Yan Du ◽  
George G. Adams ◽  
Nicol E. McGruer ◽  
Izhak Etsion
Keyword(s):  
Finite Element ◽  
Finite Element Simulations ◽  
The Impact ◽  
Theoretical Stress

Three key parameters describing contacts with adhesion were identified in previous investigations. Here a series of finite element simulations of a single load/unload cycle of a contact are performed to study the impact of each of these parameters. The results show that one parameter (S) is most important in determining the separation mode, i.e. brittle or ductile separation. Smaller S leads to brittle separation while larger S gives ductile separation. The transition between the two separation modes occurs at about S = 1.2 which corresponds to the theoretical stress being somewhat greater than the hardness.

Finite Element Modelling of Volumetric and Shear Ductile Micro- and Macro-Fracture Processes Under Long Time Loading

2008 ◽  
Author(s):  
Lucija Pajic ◽  
Alexander A. Lukyanov
Keyword(s):  
Finite Element ◽  
Pipeline Steel ◽  
Damage Model ◽  
Shear Loading ◽  
Continuous Operation ◽  
Propagation Path ◽  
Economic Implications ◽  
Long Time ◽  
Fracture Processes ◽  
Damage Tensor

Submarine and onshore pipelines transport enormous quantities of oil and gas vital to the economies of virtually all nations. Any failure to ensure safe and continuous operation of these pipelines can have serious economic implications, damage the environment and cause fatalities. A prerequisite to safe pipeline operation is to ensure their structural integrity to a high level of reliability throughout their operational lives. This integrity may be threatened by volumetric and shear ductile micro- and macro-fracture processes under long time loading or continuous operation. In this paper a mathematically consistent damage model for predicting the damage in pipeline structures under tensile and shear loading is considered. A detailed study of widely used damage models (e.g., Lemaitre’s and Gurson’s models) has been published in the literature. It has been shown that Gurson’s damage model is not able to adequately predict fracture propagation path under shear loading, whereas Lemaitre’s damage model (Lemaitre, 1985) shows good results in this case (e.g., Hambli 2001, Mkaddem et al. 2004). The opposite effect can be observed for some materials by using Gurson’s damage model in the case of tensile loading (e.g., Tvergaard and Needleman 1984; Zhang et al. 2000; Chen and Lambert 2003; Mashayekhi et al. 2007) and wiping die bending process (Mkaddem et al. 2004). Therefore, the mathematically consistent damage model which takes into account the advantages of both Lemaitre’s and Gurson’s models has been developed. The model is based on the assumption that the damage state of materials can be described by a damage tensor ωij. This allows for definition of two scalars that are ω = ωkk/3 (the volume damage) (Lukyanov, 2004) and α = ωij′ωij′ (a norm of the damage tensor deviator ωij′ = ωij −ωδij) (Lukyanov, 2004). The ω parameter describes the accumulation of micro-pore type damage (which may disappear under compression) and the parameter α describes the shear damage. The proposed damage model has been implemented into the finite element code ABAQUS by specifying the user material routine (UMAT). Based on experimental research which has been published by Lemaitre (1985), the proposed isotropic elastoplastic damage model is validated. The results for X-70 pipeline steel are also presented, discussed and future studies are outlined.

scholarly journals Characterization of Maple and Ash Material Properties for the Finite Element Modeling of Wood Baseball Bats

2018 ◽  
Vol 8 (11) ◽  
pp. 2256 ◽  
Author(s):  
Joshua Fortin-Smith ◽  
James Sherwood ◽  
Patrick Drane ◽  
David Kretschmann
Keyword(s):  
Finite Element ◽  
Finite Element Modeling ◽  
Material Properties ◽  
Charpy Impact ◽  
Impact Testing ◽  
Charpy Test ◽  
Ball Impact ◽  
Element Modeling ◽  
The Impact ◽  
Baseball Bats

To assist in developing a database of wood material properties for the finite element modeling of wood baseball bats, Charpy impact testing at strain rates comparable to those that a wood bat experiences during a bat/ball collision is completed to characterize the failure energy and strain-to-failure as a function of density and slope-of-grain (SoG) for northern white ash (Fraxinus americana) and sugar maple (Acer saccharum). Un-notched Charpy test specimens made from billets of ash and maple that span the range of densities and SoGs that are approved for making professional baseball bats are impacted on either the edge grain or face grain. High-speed video is used to capture each test event and image analysis techniques are used to determine the strain-to-failure for each test. Strain-to-failure as a function of density relations are derived and these relations are used to calculate inputs to the *MAT_WOOD (Material Model 143) and *MAT_EROSION material options in LS-DYNA for the subsequent finite element modeling of the ash and maple Charpy Impact tests and for a maple bat/ball impact. The Charpy test data show that the strain-to-failure increases with increasing density for maple but the strain-to-failure remains essentially constant over the range of densities considered in this study for ash. The flat response of the ash data suggests that ash-bat durability is less sensitive to wood density than maple-bat durability. The available SoG results suggest that density has a greater effect on the impact failure properties of the wood than SoG. However, once the wood begins to fracture, SoG plays a large role in the direction of crack propagation of the wood, thereby determining if the shape of the pieces breaking away from the bat are fairly blunt or spear-like. The finite element modeling results for the Charpy and bat/ball impacts show good correlation with the experimental data.

Relationship Between Charpy V-Notch Impact Value and Fracture Mechanics Toughness: Added Value of Finite Element Analysis and Instrumented Impact Tests

2011 ◽  
Author(s):  
Philippe Thibaux ◽  
Filip Van den Abeele ◽  
Philippe Burlot
Keyword(s):  
Finite Element ◽  
Master Curve ◽  
Impact Test ◽  
Crack Arrest ◽  
Smooth Transition ◽  
Unstable Crack ◽  
Impact Tests ◽  
The Difference ◽  
Energy Dissipated ◽  
The Impact

Each structure is designed with resistance versus the fracture, which requires the knowledge of the fracture resistance of the material. If no fracture mechanics data of the material is available, a KJC can be inferred from the master curve approach. The master curve approach relates a fracture toughness of 100 MPAm1/2 to the impact transition temperature T27J with a shift of 18°C. Although this relationship was successfully applied to a large number of experiments, some steels deviate significantly from the previous relationship, which can even lead to non-conservative design. In the present paper, instrumented impact tests (Charpy V-Notch CVN) and compact tensile (CT) tests were performed on two materials, one thermomechanically (TM-) rolled and one normalized steel. The difference between T0 and T27J was found to be different for these materials. Furthermore, the normalized steel exhibits a smooth transition from brittle to ductile behaviour, while the TM-rolled material shows a very steep transition. Extra information is gained by combining the instrumentation of the impact test and the finite element simulations of both the CT and impact tests. From the instrumented tests, it is also possible to determine the load at unstable crack propagation, the amount of energy dissipated at that moment, the load at crack arrest and the energy dissipated after crack arrest. From the finite element simulation, one learns about the constraints ahead of the crack tip for both configurations. The investigation teaches us that the smooth transition of the normalized material is related to a high energy dissipated after crack arrest, while the TM-rolled material has a much lower crack arrest load. The difference between T0 and T27J is then discussed by decomposing the total energy in the impact test between crack initiation, propagation and arrest. It is compared with KJC, which determines the toughness at unstable crack propagation, by reviewing the literature and local stress states computed from finite element.

Finite Element Modeling of Ductile Tearing of Pipeline-Steel in Cracked Plates

2004 ◽  
Author(s):  
Yu Chen ◽  
Steve Lambert
Keyword(s):  
Finite Element ◽  
Void Nucleation ◽  
Pipeline Steel ◽  
Damage Model ◽  
Tensile Load ◽  
Maximum Load ◽  
Void Coalescence ◽  
Ductile Tearing ◽  
Numerical Predictions ◽  
Measured Load

The purpose of this work was to develop a three-dimensional finite element model to simulate ductile tearing in pipeline-steels. The measured load versus displacement histories for single edge notch tension (SENT) and surfaced-cracked wide plate specimens, both made of X-70 pipeline-steel plates and subject to tensile load, were numerically predicted using the proposed damage model. In the numerical model, progressive damage was restricted to a predetermined ductile tearing zone. The material damage behaviour in this tearing zone was described in terms of a Gurson-Tvergaard (G-T) isotropic constitutive model, which accounts for micro-void nucleation and growth. The criterion for the onset of void coalescence was determined via the Thomason criterion. Experimentally measured load-displacement histories for all specimens were accurately reproduced by the proposed model, irrespective of different plate width, thickness and crack configurations. The numerical predictions were in good agreement with experimental test data in terms of both the maximum load and the corresponding displacement at maximum load. The proposed damage model was also used to numerically estimate the effect of crack growth on maximum load for these cracked specimens. The results in this paper demonstrate the potential of the proposed damage model as an engineering tool for analyzing ductile tearing in application to defect assessment of surface cracked pipes.

EFFECTS OF STRAIN RATE DEPENDENCY OF MATERIAL PROPERTIES IN LOW VELOCITY IMPACT

2008 ◽  
Vol 22 (09n11) ◽  
pp. 1165-1170 ◽  
Author(s):  
HIROFUMI MINAMOTO ◽  
ROBERT SEIFRIED ◽  
PETER EBERHARD ◽  
SHOZO KAWAMURA
Keyword(s):  
Finite Element ◽  
Strain Rate ◽  
Yield Stress ◽  
Coefficient Of Restitution ◽  
Finite Element Simulations ◽  
Material Behavior ◽  
Rate Dependency ◽  
Rate Dependent ◽  
Strain Rate Dependency ◽  
The Impact

Impact processes are often analyzed using the coefficient of restitution which represents the kinetic energy loss during impact. In this paper the effect of strain rate dependency of the yield stress on the coefficient of restitution is investigated experimentally and numerically for the impact of a steel sphere against a steel rod. Finite Element simulations using strain-rate dependent material behavior are carried out. In addition, Finite Element simulations with elastic-plastic material behavior, which ignore the strain rate dependency, are carried out as well as elastic material behavior. Comparisons between the experiments and the simulations using strain-rate dependent material behavior show good agreement, and also prove the strong dependency of the coefficient of restitution on the strain rate dependency of the yield stress for steel. The results from both, the experiments and the simulations show also the strong influence of the wave propagation in the rod on the coefficient of restitution.

Low-frequency impact sound of timber floors: A finite element–based study of conceptual designs

2020 ◽  
pp. 1351010X2091787
Author(s):  
Jörgen Olsson ◽  
Andreas Linderholt
Keyword(s):  
Finite Element ◽  
Low Frequency ◽  
Sound Transmission ◽  
Human Perception ◽  
Finite Element Simulations ◽  
Building Industry ◽  
Frequency Range ◽  
Floor Surfaces ◽  
The Impact ◽  
Selection Of

Traditionally, product development concerning acoustics in the building industry is measurement oriented. For lightweight floors, frequencies that are lower than the frequency range for heavy concrete floors are an issue. The frequency range of from 50 Hz down to 20 Hz influences the human perception of impact sound in multi-story apartment buildings with lightweight floor constructions, such as timber floors, for example. It is well known that a lower frequency range of interest makes finite element simulations more feasible. Strategies for reducing impact sound tend to be less straightforward for timber floors because they have a larger variation of designs when compared to concrete floors. This implies that reliable finite element simulations of impact sound can save time and money for the building industry. This study researches the impact sound transmission of lightweight timber floors. Frequency response functions, from forces on excitation points to sound pressure in the receiving cavity below, are calculated. By using fluid elements connected to reflection-free boundary elements under the floors in the models, the transmission and insulation can be studied without involving reverberation. A floor model with a hard screed surface will have a larger impact force than a softer floor, although this issue seems less pronounced at the lowest frequencies. To characterize floor surfaces, the point mobilities of the impact points are also calculated and presented. The vibration and sound transmission levels are dependent on the selection of the excitation points.

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