WORKSHOP 1 STATIC WELD STRENGTH …innomet.ttu.ee/martin/Mxx0060/YL5_weld_stress/Workshop_1...Goal: In this workshop, a static analysis of a two different welded joints including stress

WORKSHOP 1 STATIC WELD STRENGTH EVALUATION OF FASTENERS For ANSYS release 14

Goal: In this workshop, a static analysis of a two different welded joints including stress evaluation of the welded joint itself. A comparison against hand book calculations will be made. The following models will be studied: 1. Lap joint having weld loaded in shear 2. Lap joint having weld loaded in both shear and tension 3. T-joint subjected to tensile load of 50 MPa 4. T-joint subjected to bending (cantilever beam), bending stress is 50 MPa

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Workshop 1, static analysis lap & T-joint

1. Launch ANSYS WorkBench: a. From the Project Page, in the “File” menu select “Restore Archive” and click on

[Browse] b. Select the Workbench archive “Workshop_1_lap_and_T_joint.wbpz” and click on

[Open] c. Save the model in the training directory specified by the teacher.

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2. Open the Simulation file: • The Workbench Project page will appear. Either double-click on the “Setup”

(highlighted) to open the existing Simulation database Lap_joint_1 or right click and select “Edit”.

• Note : A stress analysis has already been set-up and the FE-mesh is also generated. Only steps regarding model setup and stress evaluation of the weld joint will be covered in this workshop.

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3. Inspect the geometry: • Select the “Geometry” branch • Note : that the weld joints are modeled as

separate parts. Also note that the weld joint is split at the weld throat resulting in that each weld is two separate volumes.

4. Review the mesh : • Select the “Mesh” branch

•

5. Inspect the loads and supports : • Select the “Static Structural(A5)” to view

applied loads and boundary conditions.

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6. Inspect modify some contact pairs: • Bonded contact is used to join the

different parts. • Since the load should go through

the weld joint, the contact pair between the fat surfaces of both plates must change type to either friction- less or frictional.

• If frictional contact is used, specify a coefficient of friction of µ=0.2

• Since the contact forces are expected to be relative low, the definition of contact stiffness (Normal Stiffness) is set to manual and use a Normal stiffness factor of 0.01

• Also set update stiffness to each iteration

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7. Prepare model for static weld strength evaluation: • Since the static weld strength evaluation is performed using a command object

(ANSYS solver commands) we must prepare the model to be able to input data to the command object.

• The preparation of the model consist of the following items (each will be covered step by step):

1. Set contact behaviour of bonded contact to asymmetric contact for weld throat. 2. Create a named selection of the area in weld throat being the contact side. 3. Create a local coordinate to define weld throat “axis” and normal direction 4. Add contact output under output controls found in analysis settings. 5. Add command object.

• Step 1: Asymmetric contact

For either or of the bonded contact pair for weld throat change behaviour to Asymmetric.

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8. Prepare model for static weld strength evaluation, continued: • Step 2: Create named selection for contact surface

Rotate the model until you can see the “red” surface of the contact pair defining the weld throat.

• Select any surface of the upper part of weld in figure to the right, Right Mouse Button (RMB) click and select “Hide body” The red surface should now be clearly visible.

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9. Prepare model for static weld strength evaluation, continued: • Step 2: Create named selection for contact surface

Select the “Red” surface and create a named selection. Enter the name: A_weld_surf_1 The number at the end of the name make it possible to study many weld joints in the same model.

• In case you can not find the icon for create named selections, go to “View”, “Toolbars” and check “Named Selections”

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10. Prepare model for static weld strength evaluation, continued: • Step 3: Create local coordinate system

on contact surface - Select the “Red” contact surface - Click on “Coordinate Systems” in tree - Click on icon for “Create Coordinate System” An new coordinate system will be created on centre of gravity of the selected surface.

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11. Prepare model for static weld strength evaluation, continued: • Step 3: Create local coordinate system

on contact surface - Next thing is that we need to orient the coordinate in such a way that the local y-axis is parallel with weld “axis” and the local z-axis is perpendicular to weld throat surface. The location of origin of the local coordinate system is arbitrary. - Use existing points and lines in model to orient the local coordinate system.

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Use point for origin

Use line to define y-axis

Use line to define x-axis

Note: The local coordinate system does not need to lay on the weld throat surface. The important thing is the direction of the x-, y- and z-axis relative to weld throat surface.

12. Prepare model for static weld strength evaluation, continued: • Step 3: Create local coordinate system on contact surface

• Last thing is do is to assign a unique coordinate system number for the local coordinate system.

• The numbering of local coordinate systems start from 12 an higher.

• Coordinate system numbers 0-11 is reserved for ANSYS solver and can not be used.

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13. Prepare model for static weld strength evaluation, continued: • Step 4: Add contact output data for post processing

• Since the static weld strength evaluation is using the forces transmitted through contact surfaces (provides best accuracy) these data must be written to the results file.

• Click on Analysis Settings in outline.

• In “Details of Analysis Settings” for “Output Controls” specify “Yes” for Contact Miscellaneous

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14. Prepare model for static weld strength evaluation, continued: • Step 5: Add results and insert command object

• Add regular results types like total deformation, von Mises stress and principal stresses.

• Add a command object, either by RMB click on Solution(A6) or select icon

• Open the text file called: commands_static_stress_plane_geometry.txt and copy all the text in the file and past it into the command object window (where the graphics normally is).

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15. Prepare model for static weld strength evaluation, continued: • Step 5, continued: Enter values as shown in figure below

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Number of local coordinate system number, 12 in this workshop

Number of divisions of weld to view local variation of weld stress

The number at the end of the named selection to identify which weld to analyse

16. Description what the command object do: • First thing is that the command object retrieves the contact forces and surface area

of all contact elements on the surface specified by the named selection. Using the forces provides the absolute best accuracy since this a direct result item and is not dependent on the mesh density. Stresses provides a less accuracy since it is a derived measure and is dependent on mesh density, element order and so on.

• The forces in the contact elements are always output in global Cartesian coordinates, so the next step is to transform the element forces into the local coordinate system to put forces in categories normal force, shear force parallel and force perpendicular to weld.

• Summing up the three force components and surface areas of each element the average normal stress and shear components for the whole weld seam can be established. The equivalent weld stress according to Eurocode 3 is calculated.

• The command object allow a study of stresses on a specified number of segments along weld in case of local geometry causes stresses to go through weld at a small portion of weld.

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17. Run the analysis

18. Review the calculated results • Study global deformations and stress results

and verify that everything look reasonable with respect to model setup.

• After successful run of command object a plot/picture should be found under the command object. Click on the “Post Output”

• The magenta curve labelled “Av_total” is the equivalent weld stress according to Eurocode 3. Cyan curve “Av_segm” is the equivalent stress for each of the eight segments requested.

• The blue curve labelled “Av_Sig_n” is referring to average normal stress in weld. “Av_S_seg” is for each segment.

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19. Results evaluation, continued • Numerical values can be retrieved from

“Solution Information” • Look for the parameters:

SHEAR_TRANS= shear stress perpendicular SHEAR_PARAL= shear stress parallel STRESS_NORM= normal stress WELD_STRESS= equivalent stress EC-3

20. Exit the simulation model and save project.

21. Open the simulation “model Lap_joint_2”

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22. Model set-up, tips and advice • The geometry is similar to previous model, but the location of the weld joints is

different. • In this both weld joints must be studied so remember the following:

• Each weld must have a separate named selection (A_weld_surf_1, A_weld_surf_2).

• Since both weld throats have the same “orientation” only one single local coordinate system is necessary.

• Each weld joint require a separate command object. Once the first command object is specified, right click in outline and duplicate and change weld id number.

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23. Comparison FE-analysis and hand book calculation

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F τ⊥=σ ⊥=0 τ//= F/(2*a*L) σweld= (3* τ//

2 )0.5

σweld= 216 MPa

F= 75000 N a= 3 mm L= 100 mm W= 100 mm t= 10 mm

L

F L

W

Using moment equilibrium about a point between the two weld roots, two shear components can be calculated: τhorizontal=F/(W*2*a) τvertical=F*t/(W*a*L) τ⊥=σ ⊥=τresultant/√2 τ//=0 σweld= (σ ⊥2

+3* τ//2 )0.5

σweld= 180 MPa

τresultant=(τhorizontal2+τvertical

2)0.5

24. Comparison FE-analysis and hand book calculation Material used is S235: Rp0.2= 235 MPa Rm= 360 MPa βw= 0.80 γM2= 1.25 Allowable stress with respect to weld equivalent stress is 360 MPa Allowable stress with respect to normal stress 259 MPa Question: Is the weld throat size a acceptable according to Eurocode 3? Answer: ................

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Weld stresses in Lap Joint 1 (MPa) Weld stresses in Lap Joint 2 (MPa)

Weld 1 & 2 Weld 1, edge large plate Weld 2, mid of surface

σweld= σ ⊥= σweld= σ ⊥= σweld= σ ⊥=

( )2

2//

22 3Mw

ufγβ

ττσ×

≤+×+ ⊥⊥

2

9.0

M

ufγ

σ ×≤⊥

25. Analysis of T-joint subjected to either tensile or bending load • In the analysis of a T-joint the tensile and bending load (cantilever beam) is

generating a nominal stress of 50 MPa in the vertical plate at the weld toe.

• What is the difference in weld stresses between the two different loading types?

26. Open either of the models T-joint on Project page

27. Model set-up, tips and advice • Suppress the contact pair between horizontal and vertical plate to avoid running a

non linear contact analysis to save time. • Only one of the weld joints need to be studied • Use copy paste of command object between environments.

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28. Comparison weld stresses due to either bending or tensile loading Discussion: Why is there a difference between hand book calculation and FEM?

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Weld stresses in T- Joint 2 (MPa)

Tensile load Bending load

σweld= σ ⊥= σweld= σ ⊥=

τ⊥=σ ⊥=44.2 Mpa σweld= (σ ⊥

2+3* τ//2 )0.5

σweld= 88 MPa

P= 75000 N a= 4 mm W= 150 mm

Documents

WORKSHOP 1 STATIC WELD STRENGTH …innomet.ttu.ee/martin/Mxx0060/YL5_weld_stress/Workshop_1...Goal: In this workshop, a static analysis of a two different welded joints including stress