Using Virtual Testing to Study the Influence of Constraint on Fracture Properties

2018 ◽  
Author(s):  
Christopher Seal ◽  
Robert Ainsworth
Keyword(s):  
Failure Strain ◽  
Fracture Behaviour ◽  
Damage Model ◽  
Compact Tension ◽  
Single Edge ◽  
Fracture Properties ◽  
Test Pieces ◽  
Sharp Crack ◽  
Edge Notch ◽  
Ct Test

This paper presents a study in which the influence of constraint is investigated using a ductile damage model based on a stress modified failure strain. This model, proposed by Oh et al, has been used to successfully predict the J-R curve of standard compact tension (CT) test pieces for a range of different materials. Further work has shown how the model can also predict the fracture behaviour of non-standard CT test specimens, in which a blunt notch is used in place of a sharp crack. Continuing on from this work, the paper predicts the J-R curves of single edge notch tension (SET) test pieces with both a sharp crack and blunt notches.

Comparison of Fatigue Crack Growth Rates Between Different Specimen Geometries

2021 ◽  
Author(s):  
Yan-Hui Zhang ◽  
Matthew Doré
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Literature Review ◽  
Crack Growth ◽  
Compact Tension ◽  
Specimen Geometry ◽  
Single Edge ◽  
Single Edge Notch ◽  
Advantages And Disadvantages ◽  
Edge Notch

Abstract Most engineering components are subjected to cyclic loading in service and design against fatigue failure is often a key consideration in design. For fracture mechanics fatigue analysis, fatigue crack growth (FCG) tests are often required to determine the relevant Paris power law parameters for the material under the environment concerned. Standards allow use of different specimen geometries for FCG tests such as compact tension (CT), centre crack tension (CCT), single edge notch bend (SENB) and single edge notch tension (SENT). However, when selecting specimen geometry for fatigue crack growth rate (FCGR) testing, there is often doubt about which specimen geometry is more appropriate and whether they give similar FCGR. There is limited work to compare the FCGR between different specimen geometries. This paper first briefly introduces the guidance on FCG test specimen geometries in standards and compares the advantages and disadvantages of these specimen geometries. A comprehensive literature review is carried out to compare the FCGR data between different specimen geometries. FCGR tests are conducted on SENB, SENT and CCT specimens of C-Mn steel to investigate any effects of specimen symmetry/asymmetry and crack constraint on FCGR. Based on the literature review and test data, it is concluded that FCGR is independent of the specimen geometries examined.

Reversing the Chell Model to Predict Using Monte Carlo Simulations the Original Fracture Toughness of Ferritic Steels

2018 ◽  
Author(s):  
Derreck Van Gelderen ◽  
Julian Booker
Keyword(s):  
Fracture Toughness ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Compact Tension ◽  
Load Cycle ◽  
Small Scale ◽  
Ferritic Steels ◽  
Single Edge ◽  
Edge Notch ◽  
Single Edge Notch Bend

Warm pre-stress (WPS) is the process of subjecting a pre-cracked component to a load cycle at a temperature higher than subsequent operating temperatures. This process is widely acknowledged as being able to enhance the load to fracture, especially in ferritic steels which exhibit lower shelf cleavage fracture. Various models exist to predict this type of enhancement, with the Chell model being one of the most widely used within industry. Previous research conducted by Van Gelderen et al. have reformulated the Chell model to create a method of undertaking Monte Carlo Simulations (MCS) to study the effect of WPS on brittle fracture. Following on from this research, the Chell model could effectively be reversed providing a means of predicting the underlying fracture toughness from experimental WPS data. It also offers the possibility of assessing whether or not a specific specimen has indeed seen an enhancement, solely based on its experimental apparent toughness post WPS. The reverse Chell model was applied to different experimental data and provided reasonable estimates of the original fracture toughness. In the same way that the traditional Chell model offers conservative estimates, the reverse Chell model also provides “reverse conservative” estimates of the original fracture toughness. It was also used to provide confidence that a typical fatigue pre-cracking procedure performed according to ASTM standard E399 would not be sufficient to induce a WPS benefit on the specimens. This type of check can be of particularly interest when manufacturing small scale specimens (small scale Single Edge Notch Bend (SENB) or miniature sized Compact Tension C(T) specimens); a practice often favoured by industry to maximise the number of tests possible.

Comparison between Fracture Behaviour of Pipe-Line Ring Specimens and Standard Specimens

2013 ◽  
Vol 577-578 ◽  
pp. 637-640 ◽  
Author(s):  
Nenad Gubeljak ◽  
Andrej Likeb ◽  
Jožef Predan ◽  
Yu. G. Matvienko
Keyword(s):  
Fracture Behaviour ◽  
Strain Relaxation ◽  
Crack Tip ◽  
Fatigue Loading ◽  
Single Edge ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Single Edge Notch ◽  
Pipe Line ◽  
Edge Notch

Thethin walled structures as pipe-line are often unsuitable for standard testingof fracture toughness. One possibility is applying non-standard modifiedspecimens with simple testing procedure, but measured fracture behaviour isconsequence of loading conditions and geometry of specimen. In this paper thedifferences in fracture behaviour of single edge notch bending (SENB) and ringpipe-line bended specimens are discussed. Especially uneven fatigue crack frontas consequence of complex fatigue loading caused different fracture behaviour,than standard single edge notch bending (SENB) specimens. The stress-strainconditions at the crack tip are analysed by finite element modelling. Thecritical crack tip opening displacement has been determined as a crack tipsurface strain-relaxation by using stereo-optical grading method. Comparisonbetween CTOD-R curves of both types of specimens shows difference in crackdriving force.

scholarly journals The Numerical Modelling Approach with a Random Distribution of Mechanical Properties for a Mismatched Weld

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5896
Author(s):  
Luka Starčevič ◽  
Nenad Gubeljak ◽  
Jožef Predan
Keyword(s):  
Random Distribution ◽  
Fracture Behaviour ◽  
Base Material ◽  
Local Variation ◽  
Element Model ◽  
Initial Crack ◽  
Single Edge ◽  
Edge Notch ◽  
Strength Material ◽  
Modelling Approach

The aim of this work was to include a local variation in material properties to simulate the fracture behaviour in a multi-pass mis-matched X-weld joint. The base material was welded with an over and under-match strength material. The local variation was represented in a finite element model with five material groups in the weld and three layers in the heat-affected zone. The groups were assigned randomly to the elements within a region. A three-point single edge notch bending (SENB) fracture mechanics specimen was analysed for two different configurations where either the initial crack is in the over or under-matched material side to simulate experimentally obtained results. The used modelling approach shows comparable crack propagation and stiffness behaviour, as well as the expected, scatter and instabilities of measured fracture behaviour in inhomogeneous welds.

The use of the C∗ parameter in predicting creep crack propagation rates

1977 ◽  
Vol 12 (3) ◽  
pp. 167-179 ◽  
Author(s):  
M P Harper ◽  
E G Ellison
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Single Edge ◽  
Single Edge Notch ◽  
Creep Crack ◽  
Edge Notch ◽  
Single Edge Notch Bend ◽  
Good Agreement

The applicability of the C∗ parameter for the prediction of creep crack propagation rates is considered. A new method for estimating C∗ is presented, the results from which show good agreement with those from an existing technique. Experimental results from creep crack growth tests, conducted on a 1 Cr Mo V steel using both compact tension and single edge notch bend specimens, indicate that good correlation with C∗ is obtained once the effects of stress redistribution become negligible. Finally, comparisons are drawn between C∗ and other possible correlating parameters, and the limitations of each approach are discussed.

ATLAS+ European Project: Prediction of Large Ductile Tearing in Piping Using Local Approach

2019 ◽  
Author(s):  
Arnaud Blouin ◽  
Stéphane Marie ◽  
Al Mahdi Remmal
Keyword(s):  
Laboratory Tests ◽  
Damage Model ◽  
Experimental Tests ◽  
Compact Tension ◽  
Theoretical Background ◽  
Bending Test ◽  
Continuum Damage ◽  
Single Edge ◽  
Local Approach ◽  
Ductile Tearing

Abstract In the frame of the European ATLAS+ project it was decided to evaluate if a continuum damage model can simulate a four-points beading test on a ferritic pipe (A508 type). In this paper, the theoretical background is presented. Then, based on finite elements analyses, the GTN model damage parameters are defined by simulating laboratory tests on Notched Tensile specimens and Compact Tension specimens. From that identification, experimental tests on Single Edge Notched Tensile specimens are simulated in order to verify if the previous parameters are able to describe a large ductile tearing. Finally, the four points bending test simulation is also presented.

scholarly journals Effects Of Specimen Size And Crack Depth Ratio On Calibration Curves For Modified Compact Tension Specimens

2015 ◽  
Vol 15 (2) ◽  
Author(s):  
Stanislav Seitl ◽  
Viliam Viszlay ◽  
Hector Cifuentes ◽  
Alfonso Canteli
Keyword(s):  
Crack Depth ◽  
Accurate Determination ◽  
Crack Propagation Rate ◽  
Compact Tension ◽  
Propagation Rate ◽  
Metallic Materials ◽  
Fracture Properties ◽  
Crack Depth Ratio ◽  
Ct Test

Abstract The compact tension (CT) test is frequently used to determine fracture properties of metallic materials, such as fracture energy, fracture toughness, crack propagation rate and J-R curves. In the case of cement based composites, a modified compact tension (MCT) specimen can be advantageously used due to the negligible stress concentration arising around the pulling dowel pins during the test. In this work, finite element calculations are used to determine the calibrations curves for the stress intensity factor K, COD, CMOD and CMOD(4), needed for an accurate determination of the fracture parameters, as a function of the ratio a/W. Nominal diameters are selected according to the used core bits between 50 mm and 300 mm.

The Effect of a Low Constraint Geometry on Measured T0 Values for a Nuclear Reactor Pressure Vessel Ferritic Steel

2018 ◽  
Author(s):  
Geena K. Rait ◽  
Catrin M. Davies ◽  
Stephen J. Garwood
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Nuclear Reactor ◽  
Compact Tension ◽  
Reactor Pressure Vessel ◽  
Single Edge ◽  
Single Edge Notch ◽  
Edge Notch ◽  
Low Constraint ◽  
Reactor Pressure

Current requirements for assessing the fracture toughness of reactor pressure vessel (RPV) ferritic steels are potentially overly conservative due to the employment of high constraint geometries such as compact tension (C(T)) or single edge notch bend, SEN(B), specimens for material testing. These high constraint conditions are not representative of the actual conditions experienced by the RPV in service. If this conservatism could be reduced, more appropriate predictions for RPV lifetime extension could become a possibility. In this study, a known low constraint geometry, single edge notch tension, SEN(T), has been tested alongside the higher constraint SEN(B) specimen in order to compare measured T0 and fracture toughness values for both cases. Finite element analyses have also been conducted for both geometries in order to measure T-stress and calculate Q values thereby allowing quantification of the level of constraint for both geometries. Eight SEN(B) and eight SEN(T) specimens were tested with dimensions 24 × 254 × 96 mm and 20 × 20 × 200 mm, respectively. Testing was conducted at sub-zero temperatures, as close to the T0 as possible, in accordance with the guidelines presented in ASTM E1921-17a. Contrary to expected behaviour the SEN(T) specimen indicated a higher (less negative) T0 then the SEN(B) specimen. The reason for these results are explored in this paper.

Acoustic Emission Monitoring During Fatigue Crack Growth in Standard C(T) and Miniature Single Edge Notch Tension Specimens

2020 ◽  
Author(s):  
Raghu V. Prakash ◽  
Chandan K. Mukhopadhyay ◽  
Prathmesh Pokharkar ◽  
Manuel Thomas
Keyword(s):  
Growth Rate ◽  
Acoustic Emission ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Compact Tension ◽  
Single Edge ◽  
Single Edge Notch ◽  
Edge Notch

Abstract The fatigue crack growth rate studies in a structural alloy has been carried out using ASTM E-647 standard compact tension (C(T)) specimens and miniature single edge notch tension specimens (SEN(T)) at two different stress ratios of 0.1 and 0.7. Standard C(T) specimen had a dimension of 63.5 × 61 × 8 mm thickness while the miniature SEN(T) specimen had a size of 20 mm effective length × 10 mm wide and 0.7 mm thickness. A starter notch of 0.5 mm was cut using wire EDM process to initiate fatigue crack growth in miniature SEN(T) specimen. A special fixture was designed for testing the miniature SEN(T) specimen. During the fatigue crack growth experiments, Acoustic Emission (AE) activity was monitored on-line using AE sensors from Physical Acoustics, Mistras Group, USA. For the experiments on standard C(T) specimens, a standard probe (R15A) of 15 mm diameter was used, while for small size compact tension specimen, a Nano30 AE probe was used. The crack growth was monitored by visual methods as well as by compliance technique. The cumulative counts and absolute energy information obtained during fatigue crack growth testing was used to correlate the crack growth rate with acoustic emission activity. Empirical fit of data was used to obtain cross-correlation between crack growth rate and AE parameters for both the specimen geometries. The study suggested that suitable selection and placement of sensors is essential to obtain good results using AE sensor technique.

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