DEFENCE DÉFENSE & Defence Research and Development Canada Recherche et développement pour la défense Canada Verification and Validation of a Single-Edge Notched Tensile Specimen Modelling Methods, Weld Geometrical Dependence, Through-Thickness Layers and Induced Bending Moments Christopher Bayley DRDC Atlantic DLP Nathan Samsonoff University of Victoria Department of Mechanical Engineering Technical Memorandum DRDC Atlantic TM 2010-215 October 2010 Defence R&D Canada – Atlantic Copy No. _____
Nathan SamsonoffUniversity of VictoriaDepartment of Mechanical Engineering
Technical Memorandum
DRDC Atlantic TM 2010-215
October 2010
Defence R&D Canada – Atlantic
Copy No. _____
This page intentionally left blank.
Verification and Validation of a Single-Edge Notched Tensile Specimen Modelling Methods, Weld Geometrical Dependence, Through-Thickness Layers and Induced Bending Moments
Christopher Bayley DRDC Atlantic DLP Nathan Samsonoff University of Victoria Department of Mechanical Engineering
Is the finite element method (FEM) a reliable and convenient method to model fractures? To examine this question, FEM models of single-edge notched tensile specimens were generated based on the geometry of their physical counterparts. A study of the number of through thickness elements was conducted to determine that eight elements provides sufficient mesh convergence with calculation times of approximately one hour. Similarly, different methods of modelling the weld geometry were investigated and show that the bottom weld of the plate should be modelled with a hemispherical weld cap, and the weld on the top of the plate with a flat-topped weld cap. Data collected during the pre-cracking of the physical test specimens reveal relatively poor correlation between the experimental and numerical strains. This poor agreement is believed to originate from inaccurate representation of the initial plate straightening moments due to inaccurate representation of the fixtures.
Résumé ….....
La méthode à éléments finis (MEF) est-elle une méthode fiable et pratique pour modéliser les fissures? Pour examiner la question, des modèles à éléments finis d’éprouvette de traction à une seule entaille ont été générées à la lumière de la géométrie de leurs contreparties physiques. Une étude portant sur le nombre d’éléments d’épaisseur a été réalisée dans le but de déterminer que huit (8) éléments fournissent suffisamment de convergence de maille avec des temps de calcul d’environ 1 (une) heure. De même, différentes méthodes permettant de modéliser la géométrie de soudure ont été examinées et montrent que la soudure au bas de la plaque devrait être modélisée à l’aide d’un bouchon hémisphérique soudé, et que la soudure sur le dessus de la plaque devrait l’être à l’aide d’un bouchon de soudure à dessus plat. Les données recueillies durant le précraquage des éprouvettes d’essais physiques révèlent une corrélation faible entre les déformations expérimentales et les déformations numériques. On estime que cette faible concordance est imputable à une représentation inadéquate des moments de redressement initiaux de la plaque, à cause d’une représentation inexacte du montage.
ii DRDC Atlantic TM 2010-215
This page intentionally left blank.
DRDC Atlantic TM 2010-215 iii
Executive summary
Verification and Validation of a Single-Edge Notched Tensile Specimen: Modelling Methods, Weld Geometrical Dependence, Through-Thickness Layers and Induced Bending Moments
Christopher Bayley; Nathan Samsonoff; DRDC Atlantic TM 2010-215; Defence R&D Canada – Atlantic; October 2010.
Introduction: Verification and validation (V&V) of numerical models is necessary to ensure that they correctly capture the structures that they represent. In particular, for the case of the Single Edge Tension specimens developed to examine the fracture behaviour of welded structures, V&V is particularly important, as the numerical models are used estimate the stress and strain states of their physical counterparts. In this way, the numerical models complement the experimental tests and provide additional information which otherwise would not be obtained from the experiments alone.
The single edge tension specimen was developed to be representative of a cracked ship structural element. Rather than examining only the metallurgical properties of the welded connection, these specimens also consider the stress concentration arising from the weld geometry, which in practice, is more representative of an actual ship structural element.
Results: One of the key features of the models developed during this phase of V&V is that they capture the geometry of their physical counterparts. A purpose developed script includes the measured weld geometry and angular mis-alignment of a master model. These models were subsequently loaded and compared with their physical counterparts.
The physical data used for this verification and validation was obtained during the fatigue pre-cracking of each specimen. It included eight strain gauges, crack mouth opening displacements, load and for one specimen, digital image correlation. The comparison of the data provide details of the influence of the specimen straightening and the boundary conditions associated with the behaviour of the fixtures and straps which attach the specimen to the load frame.
Significance: While further refinements to the numerical models are still required, their necessity is driven by an increased understanding of the testing configuration. For example, the importance of the out-of-plane displacements associated with the plate straightening were born-out by detailed examination of the physical specimen data. Without such a thorough verification process, the model predictions would inadequately define the physical boundary conditions.
Future plans: Models which examine the influence of the end constraints and boundary conditions need to be developed. Results from these enhanced models will then yield better predictions which can be used to estimate the fracture properties of single-edge notched tensile specimens.
iv DRDC Atlantic TM 2010-215
Sommaire .....
Verification and Validation of a Single-Edge Notched Tensile Specimen: Modelling Methods, Weld Geometrical Dependence, Through-Thickness Layers and Induced Bending Moments
Christopher Bayley; Nathan Samsonoff; DRDC Atlantic TM 2010-215; R & D pour la défense Canada – Atlantique; Octobre 2010.
Introduction : La vérification et la validation (V et V) des modèles numériques est nécessaire pour s’assurer qu’ils peuvent saisir correctement les structures qu’ils représentent. Plus particulièrement, dans le cas des éprouvettes de traction à une seule bordure d’entaille mis au point pour étudier le comportement de fissuration de structures soudées, la V et V est particulièrement importante, car les modèles numériques sont utilisés pour estimer l’état des contraintes et des déformations dans leurs contreparties physiques. De cette manière, les modèles numériques complètent les essais expérimentaux et fournissent des renseignements additionnels qui autrement n’auraient pas été obtenus à partir d’expériences seulement.
Les éprouvettes de traction à une seule bordure ont été mises au point dans le but d’être représentatives d’un élément structural fissuré provenant d’un navire. Plutôt que d’examiner seulement les propriétés métallurgiques du raccord soudé, on a également étudié la concentration des contraintes dans les éprouvettes qui étaient associées à la géométrie de fissure, ce qui, en pratique, est plus représentatif d’un élément structural de navire réel.
Résultats : L’une des caractéristiques clés des modèles mis au point durant cette phase de V et V est qu’elles tiennent compte de la contrepartie physique des éprouvettes. Un script à objectifs comprenait la géométrie de soudure mesurée et un désalignement angulaire du modèle original. Ces modèles ont été par la suite chargés et comparés avec leurs contreparties physiques.
Les données physiques employées pour cette V et V (vérification et validation) ont été obtenues durant la phase de précraquage de chaque éprouvette. Elles comprennent huit tensiomètres, des déplacements d’ouverture, des charges et, pour l’un des spécimens, une corrélation d’image numérique. La comparaison des données fournit des renseignements détaillés sur l’influence du redressement des éprouvettes et sur les conditions limites associées au comportement du montage et des courroies qui tiennent en place l’éprouvette sur le cadre de charge.
Portée : Bien que des améliorations ultérieures des modèles numériques soient requises, il importe de mieux comprendre le rôle des configurations d’essai. Par exemple, l’importance des déplacements hors plan associés au redressement de la plaque a été remarquée lors de l’examen détaillé des données physiques sur les éprouvettes. Sans une telle vérification, les prévisions du modèle définiraient de manière inadéquates les conditions physiques limites.
Recherches futures : Des modèles qui examinent l’influence de ces contraintes finales et conditions limites doivent être élaborés. Les résultats de ces modèles améliorés permettront de réaliser de meilleures prévisions qui pourraient être utilisées pour estimer les propriétés de fissuration d’éprouvettes de traction à entaille à une seule bordure.
DRDC Atlantic TM 2010-215 v
Table of contents
Abstract …….. ................................................................................................................................ i Résumé …..... .................................................................................................................................. i Executive summary ...................................................................................................................... iii Sommaire ..... ................................................................................................................................ iv
Table of contents ............................................................................................................................ v
List of figures ................................................................................................................................ vi List of tables ............................................................................................................................... viii 1 Introduction ............................................................................................................................. 1
2 Test Preparation and Design .................................................................................................... 2 2.1 Laser measurements...................................................................................................... 4 2.2 Fixtures ......................................................................................................................... 6 2.3 Strain Gauges ................................................................................................................ 7 2.4 Digital Image Correlation ............................................................................................. 7 2.5 Pre-cracking .................................................................................................................. 8 2.6 Magnetic Particle Inspection......................................................................................... 9
3 Modelling the Test Specimen Geometry ................................................................................ 11 3.1 Mesh Generation......................................................................................................... 11 3.2 Modelling the Weld Profile ........................................................................................ 13 3.3 Transformation Code .................................................................................................. 13 3.4 Fixtures and Straps ..................................................................................................... 14 3.5 Convergence and Simulation Time ............................................................................. 16
3.5.1 Convergence Study ....................................................................................... 16 3.5.2 Simulation Time ........................................................................................... 17
4 Comparison of FEM and Experimental Results ..................................................................... 19 4.1 Specimen gauge comparison....................................................................................... 19 4.2 Strap Gauge Comparison ............................................................................................ 21 4.3 Crack Mouth Opening Displacement .......................................................................... 24 4.4 Digital Image Correlation ........................................................................................... 24
Annex A .. Laser Scanning Plots................................................................................................... 29
Annex B .. Plate Transformation Code ......................................................................................... 33
Annex C .. Induced Bending Moments ......................................................................................... 37
Distribution list ............................................................................................................................. 43
vi DRDC Atlantic TM 2010-215
List of figures
Figure 1: Single edge tension specimen. ......................................................................................... 2
Figure 2: Side view of the weld profile showing the location of the notch and nomenclature ........ 3
Figure 3: Single edge notch specimen dimensions. The notch was located in the coarse grained heat affected zone of the weld. ........................................................................ 3
Figure 6: SENT specimen partially mounted in a 1MN servo-hydraulic test frame. ...................... 6
Figure 7: Relative locations of the strain gauges. On the heavily warped plates, additional strain gauges were applied on both the top and bottom weld surfaces. ......................... 7
Figure 8: Paint Pattern Used For Digital Image Correlation [7] – Specimen C3 ............................ 8
Figure 9: Magnetic Particle Inspection of SENT Specimen showing a crack growing from the end of the notch. ......................................................................................................... 10
Figure 10: Original Mesh and Seeds ............................................................................................. 11
Figure 11: FEM Mesh. Crack tip region has a radiating mesh ahead of the crack tip. All of the models assumed a crack length of 10.5 mm. ......................................................... 12
Figure 12: Progression of weld profiles sophistication. ................................................................ 13
Figure 13: Side view of the untransformed (top) and transformed (bottom) Finite Element Models ........................................................................................................................ 14
Figure 14: Experimental pin jointed fixture which allows in-plane rotation. The specimen is attached via metal straps. ............................................................................................ 15
Figure 15: Variation in strap models ............................................................................................ 15
Figure 16: Coordinate system. The X and Y arrows originate at the center of mass of the rigid body. .................................................................................................................. 16
Figure 17: Internal Weld Geometry for Various through Thicknesses ......................................... 16
Figure 18: Comparison of through-thickness strain gradient for models with different numbers of elements between the bottom and upper butt end strain gauge locations at 250kN. ..................................................................................................... 17
Figure 19: Computation Times for Various Layers ...................................................................... 18
Figure 20: Decomposition of a through-thickness strain into its membrane and bending components ................................................................................................................ 19
Figure 21: Comparison of strain gauges attached to the butt-end of specimen C3 during the first 500 cycles with FEM models with various rotational constraints and strap designs. ....................................................................................................................... 20
DRDC Atlantic TM 2010-215 vii
Figure 22: Comparison of membrane strain components for sample C3 with FEM simulations with various rotational end constraints and strap designs. .......................................... 20
Figure 23: Comparison of the notch side strap gauges attached to specimen C3. Symbols represent the experimental data, solid lines FEM models with abutting straps, broken lines FEM models with split straps. ................................................................ 21
Figure 24: Membrane strain components from the straps. ............................................................ 22
Figure 25: Comparison of calculated and applied loads during the first 500 cycles of loading C3. .............................................................................................................................. 23
Figure 26: In-plane and out-of-plane bending moments associated steady state cycles of loading specimen C3. ................................................................................................. 23
Figure 27: CMOD comparison for specimen C3. ......................................................................... 24
Figure 28: D.I.C. and Strain Gauge Comparison at Top Weld Butt End [7] ................................. 25
Figure 29: Principal Strain Comparison at 350kN [7]. From left to right are the flat weld, hemispherical weld, flat-topped weld, and DIC .......................................................... 26
Figure 30: Z-displacement at 350kN. a) fixture rx-fixed, b) fixture rx-free, c) DIC. .................... 26
viii DRDC Atlantic TM 2010-215
List of tables
Table 1: Summary of Plate and Weld Profiles ................................................................................ 5
Table 2: Experimental boundary conditions with reference to coordinate system shown in Figure 16. ..................................................................................................................... 6
Table 3: Slope Deviation of Through-Plate Strain Field ............................................................... 17
DRDC Atlantic TM 2010-215 1
1 Introduction
Verification and validation (V&V) of numerical models is necessary to ensure that they correctly capture the structures that they represent. In particular, for the case of the Single Edge Tension specimens developed to examine the fracture behaviour of welded structures, V&V is particularly important; as the numerical models are used estimate the stress and strain states of their physical counterparts. In this way, the numerical models complement the experimental tests and provide additional information which otherwise would not be obtained from the experiments alone.
This report endeavours to validate a series of FEM models which will be subsequently used to estimate the fracture toughness of these structural scale specimens. The FEM modelling procedures in this report is a continuation of the work conducted by Hawinkels [1]. His method for modelling the crack tip has been retained as well as large portions of his meshing method. Modelling and meshing were conducted in MSC.PATRAN and solved in LS-DYNA. The scripts written and methods used for calculating the J-integral from the FEM results have not been changed. Primary differences are in the number of through-thickness elements, incorporation of the weld and plate geometries as well as the boundary conditions.
The material used to fabricate these specimens is an HSLA (high-strength low-alloy) steel which obtains its mechanical properties from the microstructure instead of chemical makeup. Micro-alloying additions of elements such as vanadium or niobium are added to steel that usually has less than 0.2% carbon. In combination with controlled rolling, these micro-alloying elements result in a refined microstructure that has fine alloy carbides in a ferrite matrix [2]. HSLA-65 (ASTM A945 [3]) is of particular interest as a replacement for existing ship steel. Its greater strength allows for either stronger structures at the same weight or similar structures at reduced weight. HSLA-65 is highly weldable, but because of its lean chemical composition, it is more susceptible to the degradations of its mechanical properties in the weld Heat Affected Zone (HAZ). While the degradation of the HAZ toughness has been documented [5][6] the influence of this reduced fracture toughness on the structural scale is currently unknown. Typically fracture toughness tests use a highly constrained configuration which develops a tri-axial stress state at the crack tip. While these configurations provide a lower bound, they are inherently conservative. This has motivated others to examine alternative test configurations which have lower constraints and are more representative of the conditions experienced at the crack tip [4].
The single edge tension specimen was developed to be representative of a cracked ship structural element. Rather than examining only the metallurgical properties of the welded connection, these specimens also consider the stress concentration arising from the weld geometry, which in practice, is more representative of an actual ship structural element
2 DRDC Atlantic TM 2010-215
2 Test Preparation and Design
From two pre-existing batches of welds eight single edge tension specimens were machined. As seen in Figure 1, these specimens have a central transverse weld which joined two pieces of 15.8 mm HSLA-65 base plate. All of the specimens were welded using a low heat input Flux Core Arc Welding procedure with either a Mil Spec 71-T1 HYN weld consumables or a Mil Spec 101TM weld consumables [5][6]. A notch was EDM cut into one side of the specimen with the notch tip located in the heat affected zone. The location of the notch relative to the weld is shown in Figure 2. Along with showing the notch locations, it also establishes the weld nomenclature. This nomenclature is relative to the original edge preparation with a 45o bevelled or straight edge while the top and bottom of the weld are relative to the root pass.
The machine drawings of the single edge notch tension (SENT) specimen are shown in Figure 3 with four test pieces machined from each welded plate. As the welding procedures did not overly constrain the plates there resulted in significant welding induced distortion. In addition, the weld caps were not ground off.
Figure 1: Single edge tension specimen.
DRDC Atlantic TM 2010-215 3
Figure 2: Side view of the weld profile showing the location of the notch and nomenclature
Figure 3: Single edge notch specimen dimensions. The notch was located in the coarse grained
heat affected zone of the weld.
5.00 mm
1.50 mm
7.00 mm
7.50 mm
3.00 mm
1.60 mm
ø 19.05 mm
222.25 mm
57.15 mm25.40 mm
38.2
2 m
m
R 76.20 mm
152.40 mm
76.20 mm
457.
20 m
m
88.90 mm
381.
0 m
m
304.
80 m
m
4 DRDC Atlantic TM 2010-215
2.1 Laser measurements
Accurately capturing the specimen geometry is necessary to achieve a better correspondence between the measured and predicted behaviour. While the design dimensions and tolerances are known for the plates and notches, the welding process introduced significant angular distortion and misalignment.
A laser scanner consisting of a laser distance sensor mounted on linear bearings and connected to a string potentiometer was used to measure the two-dimensional profile of the plates. The system was calibrated using a number of steel blocks of various heights to obtain a calibration curve for both the laser distance sensor and the string potentiometer. Both were highly linear and a constant value to convert from volts to millimetres.
Figure 4and Figure 5 show the weld and plate surface profiles along the length of specimen A1 with the remaining specimen profiles in Annex A. The upper surfaces of the welds share a similar top-hat shape. The upper surfaces are similar in dimensions and geometry, with their maximum heights varying from 2.4 to 4.3 mm. The bottom surface of the welds are less varied than their upper surface counterparts due to the use of a ceramic backing strip that was used to support the root welding pass. With the exception of specimen C4, all the bottom welds are hemispherical with 1 to 3 mm variation in radius.
Figure 4: Laser Scanner Weld Profiles Specimen A1
A1 Weld Profiles
-12
-8
-4
0
4
8
12
-20 -15 -10 -5 0 5
Distance(mm)
Hei
ght(
mm
)
DRDC Atlantic TM 2010-215 5
Figure 5: Laser Scanner Plate Profile Specimen A1
The general plate profile along the centre longitudinal axis of each specimen is seen in Figure 5. In this scan, the extent of the angular distortion is clearly seen with the bottom surface being convex. The maximum angular misalignment of this plate is 0.75°.
A summary of the laser scanner data is listed in Table 1. With the exception of C4, all of the specimens have hemispherical shaped bottom weld profiles. The top weld profiles are varied, with the majority having two or three prominent peaks associated with each weld pass. The plate profiles follow the same general pattern with the top weld being on the concave side.
Pre-cracking of the samples was accomplished in a 1MN servo-hydraulic test frame. The SENT specimen was vertically positioned between the crosshead and the actuator as shown in Figure 6. The test piece was connected to the fixtures using a number of bolts and solid metal straps. The setup allows for in-plane rotation of the part about points 420mm from the notch while allowing limited rotation in the other two directions. As well, translational degrees of freedom in all but the vertical direction of the bottom fixture are restrained. These boundary conditions are summarized in Table 2.
Table 2: Experimental boundary conditions with reference to coordinate system shown in Figure 16.
x y z rx ry rz Upper Fixed Fixed Fixed Free Fixed Limited
Figure 6: SENT specimen partially mounted in a 1MN servo-hydraulic test frame.
Data was acquired from a number of different sources. All of the data was collected from sensors which were either attached directly to the specimens, or measured the response of the test frame.
DRDC Atlantic TM 2010-215 7
2.3 Strain Gauges
Strain gauges were applied to the bottom surface of all the plates, and the straps as shown in Figure 7. On the plates, the strain gauges were located at the intersection of a line extending 45° from the notch with the specimen’s centerline. In addition the more heavily warped plates had gauges on the top surface as well. The four outside straps were also strain gauged. All of the gauges were CEA-06-125UN-350 from Measurements Group, Inc. The signal outputs were fed into a Vishay Measurements Group 2310 signal conditioner bank. An excitation voltage of 5V was used to ensure heat output from the gauges would not affect the readings due to thermal effects. Signal conditioner gains were set based on the strains predicted by the FEM model. The amplified and filtered signal output from that was then fed into the MTS data acquisition system and captured in a data file.
a) Overall Gauge Locations b) Test Specimen Gauges
Figure 7: Relative locations of the strain gauges. On the heavily warped plates, additional strain gauges were applied on both the top and bottom weld surfaces.
2.4 Digital Image Correlation
For specimen C3, the pre-cracking coincided with a vendor demonstration of a Digital Image Correlation (DIC) system. DIC is a method of calculating strain by measuring the relative displacement of surface points. These points, as shown in Figure 8, can be either reflective markers, paint specks or anything else that is discernable from the background.
8 DRDC Atlantic TM 2010-215
Figure 8: Paint Pattern Used For Digital Image Correlation [7] – Specimen C3
DIC can be done in either one, two or three dimensions. One-dimensional DIC involves a single camera and lines painted onto a specimen. The movement of these lines is tracked and a resulting one-dimensional strain field is produced. Two-dimensional DIC involves painting a speckle pattern onto the specimen and using a single camera. The movement of these particles is tracked and their relative motion is converted into a two-dimensional strain field. Three-dimensional DIC involves the use of the same speckle pattern, but with two cameras spaced a distance apart. The differences in particle location due to parallax motion leads to high accuracy three-dimensional strain measurements. Increasing the dimensions of strain fields being measured increases the computational time due to more data and more calculations being required.
Data collection lasted for approximately 15 seconds, and data processing for about 15 minutes. Approximately 10,000 data points were generated from the speckle pattern.
2.5 Pre-cracking
Prior to testing, the specimens were installed within the test frame. This included attachment of the straps to either ends of the specimen using sixteen bolts. The specimen was first loosely mounted into place, and subsequently each bolt was tightened with a wrench to an unspecified
DRDC Atlantic TM 2010-215 9
torque value. Following the assembly of the test specimen, all of the strain gauges were zeroed and hence knowledge of the strains associated with the assembly of the test frame was not collected.
Pre-cracking was done in the spirit of ASTM 1820 [8]. This fracture standard specifies the pre-cracking of the specimen in order to generate a sharp crack which is subsequently fractured. The pre-cracking phase involves cyclically loading the specimen to one of two maximum loads based on either the known yield strength, or a fraction of the expected fracture toughness. As it turned out, the calculation for the initial pre-cracking load based on the yield strength was unsuitably low as the pre-cracking load was several orders of magnitude less than the ultimate tensile strength. The secondary pre-cracking load, which was based on Young’s Modulus, Poisson’s ratio and the J-integral value from test specimens, provided a much more reasonable number as it was about 60% of the expected tensile strength.
A maximum to minimum load ratio of 0.1 was used to cyclically load the specimens. After it was discovered that the straightening of the plate generated a compressive force on the convex side of the plate, the minimum load level was increased while leaving the maximum load untouched. However by decreasing the load range the crack failed to grow and so the original pre-cracking loads continued.
All of the pre-cracking was conducted at 10 Hz under load control. Some initial PID control tweaking was done at various frequencies and a stable and accurate signal could be maintained at 10 Hz. It was decided not to attempt higher frequencies as there were already significant vibrations through the floor and machinery.
2.6 Magnetic Particle Inspection
Measurement of the pre-cracking crack extension was done with magnetic particle inspection. This method involves spraying a fluorescent magnetic liquid within a magnetic field and viewing under a UV light. The magnetic field was applied using a handheld electromagnet which extended across the notch tip while the spray was an oil suspension of fluorescent dyed iron particles. Applying a magnetic field across the part causes a magnetic flux to flow through the part. At cracks and voids, the magnetic field is disrupted causing it to exit the part at the crack location. When the fluorescent spray is applied the particles congregate at this flux exit point as viewed in Figure 9.
10 DRDC Atlantic TM 2010-215
Figure 9: Magnetic Particle Inspection of SENT Specimen showing a crack growing from the end of the notch.
DRDC Atlantic TM 2010-215 11
3 Modelling the Test Specimen Geometry
The pre-existing FEM models were an idealization of the test specimens and did not reflect individual geometric differences between the specimens, nor the angular distortion resulting from the welding process. As well, they did not accurately represent the weld profile, instead leaving it flush with the top and bottom surfaces of the specimens. These geometric features were first measured, and then incorporated within the FEM models through a geometrical transformation script.
3.1 Mesh Generation
As a basis for all subsequent specimen specific models, a generic FEM model which captures the basic geometry of the specimens was developed in MSC.PATRAN. All of the numerical models considered a constant crack length of 10.5 mm.
Figure 10 shows the original mesh in the crack region including the necessary seeds required to manually generate the desired mesh.
Figure 10: Original Mesh and Seeds
The final mesh maintained the same circular contours around the crack tip, but otherwise used a different mesh. The six sections around the crack were regenerated using the Isomesh tool in MSC.PATRAN from the original mesh seeds. Next, the areas in the weld region were meshed using the Paver tool while making sure to set the Global Edge Length to 1. The final large section of the specimen was then meshed using the Paver tool, but this time with a Global Edge Length of 9. The remaining mesh associated with the rigid ends and straps is not as important, with the only
12 DRDC Atlantic TM 2010-215
requirement being nodal continuity between adjacent parts. Figure 11 illustrates the final FEM mesh.
The FEM mesh of the specimen was sketched in two-dimensions, and then extruded through to the final thickness. This procedure had the benefit of allowing the number of through-thickness layers to be varied without the time-consuming process of remeshing the entire model. In addition a constant through-thickness mesh facilitates the calculation of the contour integral used in the J-integral calculation since each layer has the same mesh density around the crack tip. Greater numbers of through-thickness elements were required in order to model the bevelled weld profile, along with capturing the bending stress components; however, the greater the number of elements, the greater the solution time. Decreased through-thickness layers expedite calculations, but with reduced accuracy.
Figure 11: FEM Mesh. Crack tip region has a radiating mesh ahead of the crack tip. All of the
models assumed a crack length of 10.5 mm.
DRDC Atlantic TM 2010-215 13
3.2 Modelling the Weld Profile
The weld geometry is an important feature of the test plates. As seen in Figure 2 the welds have three bumps on the top surface each associated with a weld pass, and one large bump on the bottom surface from the ceramic backing strip. These geometrical features were not considered in the original models developed by Hawinkels (Figure 12a) with only changes in the material properties to differentiate between the weld metal and the base plate. Consequently, the results from these simulations did not include the effect of the stress raisers associated with the weld profile.
a) Original Weld Profile b) Semi-Circular Arcs c) Final Weld Model with Flat Top Profile and Semi-Circular Arc Bottom
Figure 12: Progression of weld profiles sophistication.
The first attempt at modelling the weld region was to use two semicircular arcs as weld caps, as shown in Figure 12b. Compared to the physical specimen, the bottom weld is well represented by this approximation, however not the top weld surface. For this surface, a flat topped weld profile was developed as, shown in Figure 12c. This provides sharper angles at the weld boundary to more accurately represent the specimen.
3.3 Transformation Code
MSC.PATRAN was used to generate a master FEM model which does not include the weld profiles or the measured misalignment. In order to incorporate these specimen specific attributes, a script was written in GNU Octave which is listed in Annex B. This script generates specimen specific geometries with a bottom weld radius, a top weld height and angular distortion. The script takes the master FEM model as input and outputs a transformed file that maintains node and element numbering, but changes the nodal locations, as seen in Figure 13. Approximate runtime for this script was five minutes, which allowed a large variety of geometrical configurations to be run without having to change the geometry and mesh properties in MSC.PATRAN, which would have been exceedingly time consuming.
14 DRDC Atlantic TM 2010-215
Figure 13: Side view of the untransformed (top) and transformed (bottom) Finite Element Models
The transformation code operates in two stages. The first stage models the weld caps. The script searches for nodes that are on the top or bottom surface and in the appropriate weld region and then changes their z-coordinate. The result of this stage is a flat plate with accurate weld caps. Second, the script uses the inputted maximum height and linearly interpolates the z-coordinate for every node in the plate. The plate slopes down to the minimum value located at the notch. The result of this step is a plate that has z-coordinates shifted up or down according to the input value.
3.4 Fixtures and Straps
In addition to the geometrical changes to the test specimens, the boundary conditions used to represent the fixtures and straps were also modified. The experimental pin jointed fixture is shown in Figure 14. The large central pin allows in-plane rotation of the specimen, while minimizing out-of plane displacements. Between the fixture and specimen are a series of metal straps.
The original FEM meshes idealized the fixtures as a rigid link between the pin and upper surface of the specimen. This arrangement allowed for the in-plane rotation of the specimen while applying an axial load. While an elegant approach, this oversimplified the boundary conditions and did not allow for the out-of-plane rotation associated with the straightening of the plates.
DRDC Atlantic TM 2010-215 15
Figure 14: Experimental pin jointed fixture which allows in-plane rotation. The specimen is attached via metal straps.
Instead of this arrangement, the two representation of the fixtures and straps are shown in Figure 15 and include an infinitely rigid plate (shown in blue) attached to a set of linear elastic straps (shown in yellow) which are then attached to the transformed specimen (shown in red). While the straps had the same cross-sectional area as their physical counterparts they were initially modelled abutting (Figure 15a), rather than straddling the specimen and fixtures (Figure 15b).
a) Abutting Straps b) Split straps
Figure 15: Variation in strap models
On either ends of the specimen, the fixture was represented with a rigid material. In LS-DYNA the displacement and rotational constraints of rigid materials are specified at its centre of mass, and hence an appropriately sized material captures the large pin joint of the physical fixture. In order to better represent the out-of-plane rotations inherent in the bolted connections variations in the out-of plane rotation were examined. With reference to Figure 16, the rotations about x-axis
16 DRDC Atlantic TM 2010-215
and labelled as rx, while rotations about the y-axis are labelled ry and relative to the center of mass of the fixture.
Figure 16: Coordinate system. The X and Y arrows originate at the center of mass of the rigid
body.
The FEM models were solved in LS-DYNA using an implicit analysis. Material properties for both the weld and base materials were elastic-plastic obtained from actual stress-strain curves [5].
3.5 Convergence and Simulation Time
3.5.1 Convergence Study
In order to determine the optimum through-thickness mesh density a convergence study was performed in which the output from models with increase mesh density are compared. Increasing the number of elements increases the simulation time, but also increases the accuracy of the results. A number of models with the same geometry, but different numbers of through thickness layers were generated and processed, as seen in Figure 17
Figure 17: Internal Weld Geometry for Various through Thicknesses
DRDC Atlantic TM 2010-215 17
The resulting through thickness strain profiles were obtained at the location of the strain gauge on the butt end of the specimen and graphed in Figure 18 to see the convergence. In Figure 18, 0 represents the bottom surface of the plate and 16mm the top surface. Apart from the model with only two and four through thickness elements, the remaining models appear to have converged. Table 3 lists the slopes of the strain distributions compared with that obtained from the 12 elements through thickness (ett) model. Increasing the number of layers from two to four, and from four to six has a significant effect on the resulting strain profile, while further increases in the number of through-thickness elements is less significant..
Table 3: Slope Deviation of Through-Plate Strain Field
Figure 18: Comparison of through-thickness strain gradient for models with different numbers of
elements between the bottom and upper butt end strain gauge locations at 250kN.
3.5.2 Simulation Time
Prohibitively high simulation times may force the use of less accurate models. The computation times from multiple simulations were recorded and plotted in Figure 19. The computation times
0
2
4
6
8
10
12
14
16
600 700 800 900 1000 1100 1200
Strain (με)
Dep
th In
to P
late
(mm
)
2ETT4ETT6ETT8ETT10ETT12ETT
18 DRDC Atlantic TM 2010-215
are dependent on a number of criteria, not just the number of elements. The number of equations to be solved and the matrix sizes are dependent directly on the number of elements, but the iterations to convergence as well as the percentage of data that is stored in the computer’s memory or on the hard disk varies, thus resulting in a non-linear increase in computation times. Based on the compromise between accuracy and solution time eight through-thickness elements was chosen.
Figure 19: Computation Times for Various Layers
Simulation Time Comparison
0
20
40
60
80
100
120
140
160
180
0 2 4 6 8 10 12 14
Through Thickness Layers
Com
puta
tion
Tim
e (m
in)
DRDC Atlantic TM 2010-215 19
4 Comparison of FEM and Experimental Results
Validation of the finite element model is of paramount importance, as an unreliable model will not be able to accurately predict the stress and strain state at the crack tip. Therefore, a thorough validation and verification of the numerical and experimental results was required. Several measures were used to compare the models to their respective test specimens including strain gauges, axial displacement, crack mouth opening displacement and digital image correlation. For the validations phase all of the comparisons are made with a common specimen, C3.
4.1 Specimen gauge comparison
Test specimen C3 was one of the few samples which had four strain gauges. The results from these gauges were compared to the predicted FEM data. The strain gauges on the specimens typically show a linear relationship between strain and load that matches the predicted slope from the FEM. The major difference is an initial non-linearity which is believed to be associated with the straightening of the plates.
Figure 21 compares the four strain gauge locations during the first 500 cycles of pre-cracking with the monotonically loaded FEM results. While the model predicts an increasing strain with applied load, the strain gauges measured an initial non-linearity that eventually flattens out at around 50 kN. Within this linear region, the slopes of the strain gauge data and FEM predictions are essentially the same. However, the initial non-linear portion is markedly different. On the bottom surface both strain gauges are initially compressive until 150 kN is applied.
While differences exist between the predicted and measured surface strains, the difference between the predicted and measured membrane strain components shown in Figure 22 are negligible. These membrane strain components were computed by averaging the surface strain value (see Figure 20). Thus, the observed difference between the experimental and numerical predictions plotted in Figure 21 is due solely to the inadequately capturing the bending strain component.
Figure 20: Decomposition of a through-thickness strain into its membrane and bending
components
20 DRDC Atlantic TM 2010-215
Figure 21: Comparison of strain gauges attached to the butt-end of specimen C3 during the first 500 cycles with FEM models with various rotational constraints and strap designs.
Figure 22: Comparison of membrane strain components for sample C3 with FEM simulations with various rotational end constraints and strap designs.
-500
0
500
1000
1500
2000
0 50 100 150 200 250 300Applied Load (kN)
Mic
ro S
trai
nAbutting - rx & ry ConstrainedSplit - rx & ry ConstrainedSplit - ry Constrained
Bottom Surface
Top Surface
0
100
200
300
400
500
600
700
800
900
1000
0 50 100 150 200 250 300Applied Load (kN)
Mem
bran
e M
icro
Str
ain
Com
pone
nt
Abutting - rx & ry ConstrainedSplit - rx & ry ConstrainedSplit - ry Constrained
FEM
Strain Gauge Data
DRDC Atlantic TM 2010-215 21
4.2 Strap Gauge Comparison
With reference to Figure 23, the strap gauges do not fit the predicted FEM results as well as the specimen gauges. While the experimental gauges show that the straps connected to the top surface of the specimen carry a greater strain than the bottom surface strap, the opposite trend was captured in the numerical models.
Variations in the representation in the fixture rotational constraints and straps have a definite effect on the predicted strap strains, but were still found to be inadequate. As was the case for the specimen gauges, the membrane strain component is captured better than the bending strain component (see Figure 24). When examining the membrane strain component, the split straps models, rather than the abutting strap models are better at capturing the experimental trend.
Figure 23: Comparison of the notch side strap gauges attached to specimen C3. Symbols represent the experimental data, solid lines FEM models with abutting straps, broken lines FEM models with split straps.
-100
0
100
200
300
400
500
0 50 100 150 200 250 300
Applied Load (kN)
Mic
ro S
trai
n
Abutting - rx & ry ConstrainedSplit - rx & ry ConstrainedSplit - ry Constrained
Ave. Bottom Straps
Ave. Top Straps
22 DRDC Atlantic TM 2010-215
Figure 24: Membrane strain components from the straps.
The boundary conditions associated with the straps can be inferred experimentally from the four strap strain gauges. This includes the applied load and the bending moments associated with the out-of-plane straightening of the specimen and the in-plane bending moment associated with the rotation of the specimen. All of these measures can be estimated from the strain gauge data according to:
Where A is the cross sectional area of the straps, E Young’s Modulus and the average strain difference, and l the lever length. The factor C is either 4 or 2 depending on whether the out-of-plane or in-plane moments are of interest.
The calculated strap force as function of applied load is plotted in Figure 25, which is clearly seen to fail a self consistent check whereby the calculated and applied loads are not equal. From these same strain gauges, the calculated in-plane and out-plane bending moments are plotted in Figure 26. A stable hysteresis is clearly seen between the loading and unloading portion of the loading cycle for both bending moments. The out-of-plane moment is consistently greater than the in-plane moment. For the in-plane moment, the non-linear behaviour during either the loading or un-loading segment is likely caused by a combination of friction within the pinned fixture, and straps.
0
50
100
150
200
250
300
350
0 50 100 150 200 250 300
Applied Load (kN)
Mem
bran
e M
icro
Str
ain
Com
pone
ntAbutting - rx & ry ConstrainedSplit - rx & ry ConstrainedSplit - ry Constrained
Strain Gauge Data
DRDC Atlantic TM 2010-215 23
Figure 25: Comparison of calculated and applied loads during the first 500 cycles of loading C3.
Figure 26: In-plane and out-of-plane bending moments associated steady state cycles of loading specimen C3.
0
50
100
150
200
250
0 50 100 150 200 250Applied Load (kN)
Cal
culu
ated
Loa
d (k
N)
(1:1)
-200
0
200
400
600
800
1000
1200
1400
1600
1800
0 50 100 150 200 250 300
Applied Load (kN)
Mom
ent (
kN-m
m)
Out-of-Plane
In-Plane
Loading
Unloading
Loading
Loading
Unloading
24 DRDC Atlantic TM 2010-215
4.3 Crack Mouth Opening Displacement
The crack mouth opening displacement (CMOD) measurement is the distance across the crack mouth. While both the physical and the FEM results are found to be linear in Figure 27, they have different slopes, likely due to the difference in crack lengths assumed in each case. In the numerical models, little difference is found between the different fixture constrains and strap modelling approaches.
Figure 27: CMOD comparison for specimen C3.
4.4 Digital Image Correlation
The digital image correlation technique provides a full field analysis of parts of a surface without requiring large number of strain gauges. Its capability is demonstrated in Figure 28 which plots the top surface strain at the gauge location for all three methods, DIC, FEM and strain gauge. Remarkably the DIC and strain gauge data match up almost perfectly, while the FEM predictions are missing the initial non-linearity. The noise in the DIC data suggests either there is noise in the images being used for the calculation or an inherent difficulty in the method analyzing low strain values.
Figure 28: D.I.C. and Strain Gauge Comparison at Top Weld Butt End [7]
The ability of DIC to examine an area, rather than discrete point is exploited in Figure 29 which compares the influence of different weld cap models to the experimental counterpart. From left to right the models are: flat weld, hemispherical-topped weld, flat-topped weld, and DIC. All of the images utilize the same scale and colouring scheme for the fringes. Comparison of the images shows the importance of properly capturing not only the weld metal mechanical properties but also its shape. Comparisons between the flat-topped and DIC image reveal similar strain values in the weld, but with significant differences along the weld toe. While the FEM models predict a weld toe strain concentration, it is different in both magnitude and extent. Moving away from the weld region, higher strains are measured by the DIC method than FEM. This difference is likely due to the unaccounted bending moment in the FEM model.
26 DRDC Atlantic TM 2010-215
Figure 29: Principal Strain Comparison at 350kN [7]. From left to right are the flat weld,
hemispherical weld, flat-topped weld, and DIC
Figure 30 compares the z-displacement fields from two FEM models and DIC. The two FEM models consider differences in the fixture rotational constraints, with rx fixed in Figure 30a, and free in Figure 30b. It is noted that the restraint conditions result in different distributions, with the case of the rx fixed having a similar distribution but different magnitude to the experimental case. In these two figures, the largest z-displacement radiates away from the crack mouth. Noteworthy too, is that even at 350 kN, the z-displacements are significantly less than the original peak heights, indicating that the plates are not yet straight. For specimen C3, this peak height was 4.3mm, while DIC measures a maximum 2.45mm and the constrained case only 0.83mm. This large difference motivated the examination of how the fixture rotational constraints influence the out-of-plane displacement.
a) FEM b) FEM c) DIC
Figure 30: Z-displacement at 350kN. a) fixture rx-fixed, b) fixture rx-free, c) DIC.
DRDC Atlantic TM 2010-215 27
5 Conclusions
Numerical modes which include a geometrical representation of the actual welded profile were developed. These models included not only the weld geometry, but also the weld metal mechanical properties along with angular distortion associated with the welding. The results from these models were compared with their physical counterparts during pre-cracking. From these comparisons the following conclusions are drawn:
• The models capture the membrane strain component associated with the axial extension of the specimens.
• The models do not capture the straightening of the plates, with poor agreement observed by both the out-of-plane displacements and the bending strain components of the specimen. An investigation into different fixture rotational constraints showed that the problem with the FEM model lies in the rotational limits of the fixtures and straps. Changing the rotational constraints influenced the model response but did not result in a satisfactory agreement between the strain gauge and FEM data.
• The representation of the straps in the model is inadequate. Modelling the straps as rigid connection between the specimen and the fixtures does not allow for the limited amount of rotation found in the test set up.
• The strain gauges mounted on the surface straps indicate that the specimen is subjected to both in-plane and out-of-plane bending moments.
• Digital Image Correlation measurements acquired during the loading of a single specimen were found to correlate very closely with the strain gauge data, but neither method matches with the FEM model. This suggests that the problem is definitely with the FEM model not capturing some of the loading characteristics of the plate, rather than the strain gauges being improperly calibrated, or misinterpreted.
• Each of the specimens were pre-cracked until visible cracks extended from the edge of the notches. However due to the straightening of the specimens, the crack growth was not uniform. The crack lengths were consistently greater on the concave surface of the weld which coincides with the surface which was in tension rather than compression during the initial straightening of the specimens.
28 DRDC Atlantic TM 2010-215
References .....
[1] R.J.H. Hawinkels and C.J. Bayley, Numerical Fracture Evaluation of a Large Scale Tensile Test. DRDC Atlantic, March 2009.
[2] G. Krauss, Steels: Heat Treatment and Processing Principles, 1990.
[3] ASTM A945/A945m Standard Specification for High-Strength Low-Alloy Structural Steel Plate with Low Carbon and Restricted Sulfur for Improved Weldability, Formability, and Toughness, USA, 1.04 Iron and Steel Products, ASTM, 2005
[4] Sumpter, J.D.G. and Caudrey, A.J., Recommended Fracture Toughness for Ship Hull Steel and Weld. Marine Structures, 1995. 8: p. 345-357.
[5] C.J. Bayley and A. Mantei, The Influence of Heat Input on the Fracture and Metallurgical Properties of HSLA-65 Steel Welds. DRDC Atlantic, TM 2008-130, July 2008.
[6] N. Pussegoda, Fracture Toughness Characterization of HSLA Steel Weldments. DRDC Atlantic CR 2008-178, October 2008.
[7] V. Tran, SENT Specimen Study of 3D Deformation and Strain Measurements with 3D Image Correlation (ARAMIS). Trilion Quality Systems LLC, December 2009.
[8] Standard Test Method for Measurement of Fracture Toughness, ASTM E1820, 2002.
DRDC Atlantic TM 2010-215 29
Annex A Laser Scanning Plots
30 DRDC Atlantic TM 2010-215
DRDC Atlantic TM 2010-215 31
32 DRDC Atlantic TM 2010-215
DRDC Atlantic TM 2010-215 33
Annex B Plate Transformation Code
%weldtransform.m %author: Nathan Samsonoff %date: November 18th, 2009 %description: feed in ascii data file. code will edit data regarding node locations according to radius input. %%%%%CONSTANTS%%%%% DATA_FILE="fullfusion105.key"; TEXT_STOP="*ELEMENT_SOLID"; TEXT_STOP2="*PART"; WELD_START_TOP=0; WELD_END_TOP=22; WELD_START_BOTTOM=0; WELD_END_BOTTOM=6; PLATE_MAX_LENGTH=228.6; PLATE_MIN_LENGTH=-228.6; toprad=(WELD_END_TOP-WELD_START_TOP)/2; botrad=(WELD_END_BOTTOM-WELD_START_BOTTOM)/2; topmid=(WELD_END_TOP+WELD_START_TOP)/2; botmid=(WELD_END_BOTTOM+WELD_START_BOTTOM)/2; %%%%%USER INPUT%%%%% printf("Please enter top weld height (in mm & <%d): \n",toprad); WELD_HEIGHT_TOP = input(""); if(WELD_HEIGHT_TOP>toprad) disp("Please enter a valid top weld height"); fflush(stderr); break; endif printf("Please enter bottom weld radius (in mm & >%d): \n",botrad); WELD_RADIUS_BOTTOM = input(""); printf("Please enter maximum height above parallel: \n"); PLATE_HEIGHT = input(""); disp("Working..."); fflush(stdout); bottom_offset=sqrt(WELD_RADIUS_BOTTOM^2-botrad^2); %%%%%BACKUP ORIGINAL FILE%%%%% copyfeed = fopen(DATA_FILE,"r+"); copyfile = fopen("backup_fullfusion105.key","w"); while(!feof(copyfeed)) copyline = fgets(copyfeed); fprintf(copyfile,copyline); endwhile fclose(copyfeed); fclose(copyfile); %%%%%DATA READING AND SAVING TO TEMP FILE%%%%% nodedata = fopen(DATA_FILE,"r+"); %open file tempprint = fopen("tempdata.key","w"); tempprint2 = fopen("tempdata2.key","w"); fprintf(tempprint2,"$ file edited by weldtranform.m script\n"); fprintf(tempprint2,"$ bottom weld radius used is %fmm\n",WELD_RADIUS_BOTTOM); fprintf(tempprint2,"$ top weld height used is %fmm\n",WELD_HEIGHT_TOP); fprintf(tempprint2,"$ maximum height above parallel is %fmm\n",PLATE_HEIGHT); line = fgetl(nodedata); %skip header fprintf(tempprint2,line);
34 DRDC Atlantic TM 2010-215
fprintf(tempprint2,"\n"); comp = TEXT_STOP; comp2 = TEXT_STOP2; %string to stop reading at while(!strncmp(line,comp,3) && !strncmp(line,comp2,3) && !feof(nodedata)) %stop at comp or end of file line=fgetl(nodedata); %get next line without line terminator if(!strncmp(line,comp,3) && !strncmp(line,comp2,3) ) %make sure line isnt the stopping point fprintf(tempprint,line); %output line fprintf(tempprint,"\n"); %add line terminator endif endwhile %%%%%READING CLEANUP%%%%% fclose(tempprint); %close write stream %%%%%DATA EDIT AND WRITING%%%%% tempprint = fopen("tempdata.key","r+"); %reopen file for reading while(!feof(tempprint)) %stop at end of file line2=fgetl(tempprint); %get next line without line terminator temp1=deblank(substr(line2,1,8)); %cut out section of string of interest, remove trailing blanks temp2=deblank(substr(line2,9,16)); temp3=deblank(substr(line2,25,16)); temp4=deblank(substr(line2,41,16)); temp1=substr(temp1,rindex(temp1," ")+1); %find last space, cut out data afterwords temp2=substr(temp2,rindex(temp2," ")+1); temp3=substr(temp3,rindex(temp3," ")+1); temp4=substr(temp4,rindex(temp4," ")+1); int1 = str2num(temp1); %node number int2 = str2num(temp2); %perpendicular to load int3 = str2num(temp3); %parallel to load int4 = str2num(temp4); %height switch int4 case 0 %check if on bottom if(WELD_RADIUS_BOTTOM>botrad) if(int3>=WELD_START_BOTTOM & int3<=WELD_END_BOTTOM) int4=int4-sqrt(WELD_RADIUS_BOTTOM^2-(int3-botmid)^2)+bottom_offset; %outputs altered locations in proper formatting endif endif case 16 %check if on top %near notch if(int3>=WELD_START_TOP & int3<=WELD_START_TOP+WELD_HEIGHT_TOP) int4=int4 + sqrt(WELD_HEIGHT_TOP^2-(-int3-WELD_START_TOP+WELD_HEIGHT_TOP)^2); endif %middle if(int3>WELD_START_TOP + WELD_HEIGHT_TOP & int3<WELD_END_TOP - WELD_HEIGHT_TOP) int4=int4+WELD_HEIGHT_TOP;
DRDC Atlantic TM 2010-215 35
endif %away from notch if(int3>=WELD_END_TOP - WELD_HEIGHT_TOP & int3<=WELD_END_TOP) int4=int4 + sqrt(WELD_HEIGHT_TOP^2-(int3-WELD_END_TOP+WELD_HEIGHT_TOP)^2); endif endswitch %shift plates according to plate warp if(int3<100 && int3>-100) if(int3>botmid & int3<=PLATE_MAX_LENGTH) int4=int4+( (PLATE_MAX_LENGTH-int3)/(PLATE_MAX_LENGTH-botmid)*PLATE_HEIGHT ); endif if(int3<=botmid & int3>=PLATE_MIN_LENGTH) int4=int4+( (-PLATE_MIN_LENGTH+int3)/(-PLATE_MIN_LENGTH+botmid)*PLATE_HEIGHT ); endif else if(int4<=16.1 && int4>=-0.1) if(int3>botmid & int3<=PLATE_MAX_LENGTH) int4=int4+( (PLATE_MAX_LENGTH-int3)/(PLATE_MAX_LENGTH-botmid)*PLATE_HEIGHT ); endif if(int3<=botmid & int3>=PLATE_MIN_LENGTH) int4=int4+( (-PLATE_MIN_LENGTH+int3)/(-PLATE_MIN_LENGTH+botmid)*PLATE_HEIGHT ); endif endif endif %plate offset fprintf(tempprint2,"%8d%16.4f%16.4f%16.4f\n",int1,int2,int3,int4); endwhile fprintf(tempprint2,line); %print last buffered line from data file fprintf(tempprint2,"\n"); while(!feof(nodedata)) %while not end of data file line = fgets(nodedata); %just print rest out directly fprintf(tempprint2,line); endwhile %%%%%WRITING CLEANUP%%%%% fclose(tempprint); %close temp1 unlink("tempdata.key"); %delete temp1 fclose(tempprint2); %close temp2 fclose(nodedata); unlink(DATA_FILE); %delete original data file copyfeed2 = fopen("tempdata2.key","r+");%copy data from tempdata2 into the original file copyfile2 = fopen(DATA_FILE,"w"); while(!feof(copyfeed2)) copyline = fgetl(copyfeed2); fprintf(copyfile2,copyline); fprintf(copyfile2,"\n"); endwhile fclose(copyfeed2); fclose(copyfile2); unlink("tempdata2.key"); disp("Complete");
1 DRDKIM 1 DMSS 2-4-3 Materials and Welding Engineer: (Attn Dr. J. Huang)
LSTL, 555 blvd de la Carriere, 5-WB06 NDHQ - 101 Colonel By Dr Ottawa ON K1A 0K2
1 Library and Archives Canada, Atten: Military Archivist, Governments Records Branch
3 TOTAL LIST PART 2
8 TOTAL COPIES REQUIRED
44 DRDC Atlantic TM 2010-215
This page intentionally left blank.
DOCUMENT CONTROL DATA (Security classification of title, body of abstract and indexing annotation must be entered when the overall document is classified)
1. ORIGINATOR (The name and address of the organization preparing the document. Organizations for whom the document was prepared, e.g. Centre sponsoring a contractor's report, or tasking agency, are entered in section 8.) Defence R&D Canada – Atlantic 9 Grove Street P.O. Box 1012 Dartmouth, Nova Scotia B2Y 3Z7
2. SECURITY CLASSIFICATION (Overall security classification of the document including special warning terms if applicable.)
UNCLASSIFIED
3. TITLE (The complete document title as indicated on the title page. Its classification should be indicated by the appropriate abbreviation (S, C or U) in parentheses after the title.) Verification and Validation of a Single-Edge Notched Tensile Specimen: Modelling Methods, Weld Geometrical Dependence, Through-Thickness Layers and Induced Bending Moments
4. AUTHORS (last name, followed by initials – ranks, titles, etc. not to be used) Bayley, C.J.; Samsonoff, N.
5. DATE OF PUBLICATION (Month and year of publication of document.) October 2010
6a. NO. OF PAGES (Total containing information, including Annexes, Appendices, etc.)
56
6b. NO. OF REFS (Total cited in document.)
8 7. DESCRIPTIVE NOTES (The category of the document, e.g. technical report, technical note or memorandum. If appropriate, enter the type of report,
e.g. interim, progress, summary, annual or final. Give the inclusive dates when a specific reporting period is covered.) Technical Memorandum
8. SPONSORING ACTIVITY (The name of the department project office or laboratory sponsoring the research and development – include address.) Defence R&D Canada – Atlantic 9 Grove Street P.O. Box 1012 Dartmouth, Nova Scotia B2Y 3Z7
9a. PROJECT OR GRANT NO. (If appropriate, the applicable research and development project or grant number under which the document was written. Please specify whether project or grant.)
11gu05
9b. CONTRACT NO. (If appropriate, the applicable number under which the document was written.)
10a. ORIGINATOR'S DOCUMENT NUMBER (The official document number by which the document is identified by the originating activity. This number must be unique to this document.) DRDC Atlantic TM 2010-215
10b. OTHER DOCUMENT NO(s). (Any other numbers which may be assigned this document either by the originator or by the sponsor.)
11. DOCUMENT AVAILABILITY (Any limitations on further dissemination of the document, other than those imposed by security classification.)
Unlimited
12. DOCUMENT ANNOUNCEMENT (Any limitation to the bibliographic announcement of this document. This will normally correspond to the Document Availability (11). However, where further distribution (beyond the audience specified in (11) is possible, a wider announcement audience may be selected.)) Unlimited
13. ABSTRACT (A brief and factual summary of the document. It may also appear elsewhere in the body of the document itself. It is highly desirable that the abstract of classified documents be unclassified. Each paragraph of the abstract shall begin with an indication of the security classification of the information in the paragraph (unless the document itself is unclassified) represented as (S), (C), (R), or (U). It is not necessary to include here abstracts in both official languages unless the text is bilingual.)
Is the finite element method (FEM) a reliable and convenient method to model fractures? To examine this question, FEM models of single-edge notched tensile specimens were generated based on the geometry of their physical counterparts. A study of the number of through thickness elements was conducted to determine that eight elements provides sufficient mesh convergence with calculation times of approximately one hour. Similarly, different methods of modelling the weld geometry were investigated and show that the bottom weld of the plate should be modelled with a hemispherical weld cap, and the weld on the top of the plate with a flat-topped weld cap. Data collected during the pre-cracking of the physical test specimens reveal relatively poor correlation between the experimental and numerical strains. This poor agreement is believed to originate from inaccurate representation of the initial plate straightening moments due to inaccurate representation of the fixtures.
La méthode à éléments finis (MEF) est-elle une méthode fiable et pratique pour modéliser les fissures? Pour examiner la question, des modèles à éléments finis d’éprouvette de traction à une seule entaille ont été générées à la lumière de la géométrie de leurs contreparties physiques. Une étude portant sur le nombre d’éléments d’épaisseur a été réalisée dans le but de déterminer que huit (8) éléments fournissent suffisamment de convergence de maille avec des temps de calcul d’environ 1 (une) heure. De même, différentes méthodes permettant de modéliser la géométrie de soudure ont été examinées et montrent que la soudure au bas de la plaque devrait être modélisée à l’aide d’un bouchon hémisphérique soudé, et que la soudure sur le dessus de la plaque devrait l’être à l’aide d’un bouchon de soudure à dessus plat. Les données recueillies durant le précraquage des éprouvettes d’essais physiques révèlent une corrélation faible entre les déformations expérimentales et les déformations numériques. On estime que cette faible concordance est imputable à une représentation inadéquate des moments de redressement initiaux de la plaque, à cause d’une représentation inexacte du montage.
14. KEYWORDS, DESCRIPTORS or IDENTIFIERS (Technically meaningful terms or short phrases that characterize a document and could be helpful in cataloguing the document. They should be selected so that no security classification is required. Identifiers, such as equipment model designation, trade name, military project code name, geographic location may also be included. If possible keywords should be selected from a published thesaurus, e.g. Thesaurus of Engineering and Scientific Terms (TEST) and that thesaurus identified. If it is not possible to select indexing terms which are Unclassified, the classification of each should be indicated as with the title.) HSLA-65; FEM; Fracture Toughness; Fatigue
![Data Validation and Verification [Autosaved] · ON IP DATA VALIDATION, VERIFICATION AND EXCHANGE DATA VALIDATION AND VERIFICATION USING IPOBSD’S TOOLS. Data Quality Vicious Cycle.](https://static.documents.pub/doc/80x56/5e9d0eaef4fa863d2d614a6c/data-validation-and-verification-autosaved-on-ip-data-validation-verification.jpg)
