Documentation, ASMEFatigue Documentation V190

www.edrmedeso.com

ASME Fatigue ANSYS Mechanical Application

DOCUMENTATION

Extension version 201.4 Release date 13-Aug-21 Compatible ANSYS version 2020R1-R2

ASME Fatigue - Documentation – v.201.4 -13-Aug-21

- 2 -

Table of Contents

1 INTRODUCTION ......................................................................................................... 3

2 PRODUCT RESTRICTIONS ........................................................................................... 3

3 GETTING STARTED ..................................................................................................... 4

3.1 INSTALLATION ................................................................................................................. 4

3.2 LOADING EXTENSION ........................................................................................................ 6

3.3 UNINSTALLING ................................................................................................................ 6

4 ASME FATIGUE APP ................................................................................................... 8

4.1.1 Background ............................................................................................................. 8

4.1.2 Solution ................................................................................................................... 8

4.1.3 Usage ...................................................................................................................... 8

4.1.4 Issues and Limitations .......................................................................................... 11

5 REFERENCES ............................................................................................................ 12

APPENDIX A. EXAMPLE ................................................................................................... 13

APPENDIX B. IMPLEMENTATION ..................................................................................... 20

APPENDIX C. GENERAL ISSUES AND LIMITATIONS ............................................................ 21


- 3 -

1 Introduction

This application has been created using ACT (ANSYS Customization Toolkit), which provides an API (Application Programming Interface) to several ANSYS Workbench modules, including ANSYS Mechanical, ANSYS DesignModeler and ANSYS DesignXplorer. With ACT, the GUI (Graphical User Interface) of ANSYS Mechanical can be extended with new buttons. These buttons have customizable behaviour, which allows the developer to create new features, or re-use existing functionality that previously had to be included via APDL command objects. A few of the advantages with ACT include:

• Consistent handling of unit systems

• Manage user inputs

• Access to the Mechanical database as well as the ANSYS database and results

• Use Mechanicals graphics library for on-screen representation

• Shield the user from APDL code

• Create installable binary files, protecting intellectual property

2 Product Restrictions

The ASME Fatigue app described in this document utilize functionality in ANSYS that may or may not be available depending on the available ANSYS license level. The product restrictions are summarized in Table 2-1.

Table 2-1: Required ANSYS license level for the ASME Fatigue app

ANSYS license level (current) Product code Compatibility [Y/N]

DesignSpace caewbpl3 Y

Mechanical Pro mech_1 Y

Mechanical Premium mech_2 Y

Mechanical Enterprise ansys Y

ANSYS license level (legacy)

Professional NLT prf Y

Professional NLS prfnls Y

Structural struct Y


- 4 -

3 Getting Started

3.1 Installation

To install the extension, open ANSYS Workbench. On the project page, navigate to ACT Start Page > Manage Extensions and press the ‘+’ icon to install a new extension (see Figure 3-1).

Figure 3-1: Navigating to the Manage Extensions page and installing a new extension

In the browsing window that appears, select the binary extension file (.wbex file) downloaded from ANSYS app store (see Figure 3-2).

Verify that the correct extension appears in the list in the Extension Manager by going to ACT Start Page > Manage Extensions... (see Figure 3-3).


- 5 -

Figure 3-2: Select the .wbex file downloaded from ANSYS app store

Figure 3-3 The newly installed extension should appear in the Extension Manager page


- 6 -

3.2 Loading Extension

To use the extension in a project, simply click on the extension on the Extension Manager page. The extension will highlight in green when properly loaded. Mechanical needs to be closed before the loading is effective, so close Mechanical if this is open.

Several extensions can be loaded into the same project. Once the project is saved with an extension, it will load automatically with the project, so this procedure only needs to be done once per project.

Figure 3-4: Properly loaded extension on the Extension Manager page

To unload the extension, open the Extension Manager page and click on the extension again. The extension is unloaded when the green highlighting disappears.

3.3 Uninstalling

To uninstall the extension, use the Extension Manager as described in section 3.1 and 0. From the drop-down menu on the bottom right of the extension, select Uninstall.


- 7 -

Figure 3-5: Uninstalling an extension from the Extension Manager page


- 8 -

4 ASME Fatigue app

4.1.1 Background

The fatigue calculation according to ASME 2017 Sec. VIII Div.2 Part 5. Chapter 5.5.3; Fatigue assessment – elastic stress analysis and equivalent stress can be done by hand, extracting stress results at nodes for each load case. However, in addition to be a time-consuming task with risk of errors, the node location of the maximum damage cannot be known before the actual fatigue damage calculation.

4.1.2 Solution

The Fatigue (ASME VIII Div.2) result object can be used as an efficient post-processing tool to plot the number of cycles to failure, or accumulated damage according to (1) ASME 2017 Sec. VIII Div.2 Part 5 Chapter 5.5.3, for a single, or a combination of, load cases.

The fatigue curve data tables are implemented, and the fatigue curve is directly built using the material properties of the selected bodies.

4.1.3 Usage

The Fatigue (ASME VIII Div.2) result object can be applied in any Static Structural or Transient Structural analysis. The properties must be selected or entered regarding how to the results should be calculated. All properties are defined in Table 4-1. The result can be scoped to any type of geometry, but not to mesh entities (directly or through named selections).

The user can select to plot the Accumulated Damage, Cycles to Failure and log10 Cycles to Failure, calculated as described in Appendix B. If the geometry contains shell elements, the selected shell location will be used as a uniform contour through the thickness.

The fatigue curve can be the same for all bodies of the geometry selection or body dependent by selecting No for Same Curve for All Bodies. In the case of body dependent fatigue curve, the Fatigue Curve Table must be filled in. It is not possible to select No if the geometry selection contains a single body.

The result can be calculated for a single, or a combination of, load cases by selecting Yes or No for Load Case Combination. In case of a load case combination, the Load Case Table will have to be filled in. See Appendix C if the table does not pop up. A load case is defined as a range from one load step to another load step in the same analysis. Any analysis sharing the Model cell in Workbench can be used as a load case, but only solved analyses are valid.

Start Step and End Step, specified by the user, defines one load cycle, or stress range. A stress range is the two extremes of a cycle and the stress amplitude is one half of the stress range. Thus, the simulation must include a full load cycle. Note that the time for a chosen step is the end step time. Step 0 is used to define the initial time 0.

An example of property set and result is shown in Figure 4-1.


- 9 -

The fatigue curves used for the calculations are saved in the solver files directory if Yes is selected for Save Fatigue Curve, see Appendix B. It is recommended always to check if the fatigue curve has been calculated as expected.

Figure 4-1: Details and graphic view of a Fatigue (ASME VIII Div.2) result object.


- 10 -

Table 4-1: Summary of properties of the Fatigue (ASME VIII Div.2) result object (grey cells are read-only properties).

Scope

Geometry Result geometry scope, can be edges, vertices, faces or bodies

Shell Specify whether Top, Bottom or Middle results are displayed for shell bodies. This option should be ignored if only solid bodies are selected.

Definition

Result Specify whether Damage, Cycles To Failure or Logarithm Of Cycles To Failure To Base 10 should be displayed

Load Case Combination Specify whether this is a single load case, or a combination of load cases. Any analysis sharing the Model cell in Workbench can be used as a load case, but only solved analyses are valid.

Temperature Temperature at which the Young’s Modulus is extracted or interpolated for temperature dependent Young’s Modulus

Start Step Specify the start and end step defining one cycle. The stress component range will be calculated as the stress at end step minus stress at start step. The end time of the step is used. Step 0 corresponds to time step 0 End Step

Number Of Cycles Number of cycles to calculate the damage

K_f, Fatigue Strength Reduction Factor

Specify ASME fatigue strength reduction factor, default factor is 1.0

K_e, Fatigue Penalty Factor

Specify ASME fatigue penalty factor, default factor is 1.0

Load Case Table Define load case combination. Temperature, Start Step, End Step, Number of Cycles, fatigue factors and Temperature are to be defined per load case in case of load case combination.

Fatigue Curve

Same Curve For All Bodies

Specify whether the fatigue curve is the same for all selected bodies or not

Fatigue Curve (App. 3-F) Specify the Appendix 3-F table from which the fatigue coefficients are found

Fatigue Curve Table (App. 3-F)

Specify the Appendix 3-F table from which the fatigue coefficients are found by body ID (see Appendix C for body ID description)

Save Fatigue Curves Specify whether the fatigue curve should be saved to the Solver Files Directory or not

Integration Point Results

Display Option Specify whether the results at nodes are displayed as Averaged (default) or Unaveraged result

Information

Young’s Modulus Table Young’s Modulus used for the calculation (see Appendix C for body ID description)


- 11 -

Cycles To Failure Minimum number of cycles to failure, displayed per load case in the Load Case Table in case of load case combination.

Damage Maximum damage, displayed per load case in the Load Case Table in case of load case combination.

Definition

By Not to be used

Display Time Not to be used

Result Set Not to be used

4.1.4 Issues and Limitations

The Fatigue (ASME VIII Div.2) result object is limited to 3D Static Structural and Transient Structural analyses.

If a .csv file is opened or previewed while a result is being evaluated where this file will be overwritten, the evaluation will fail. The file should be closed.

Results cannot be displayed by Maximum over Time, or Time of Maximum.

If the result object is inserted under an unsolved analysis and the analysis is included to define a load case in a Load Case Table, the Load Case Table will be invalid. Thus, it will not be possible to solve the analysis. The result object will have to be either supressed or deleted before the analysis can be solved.

If the scoping method is set to All Bodies, but the geometry contains only one body, Same Curve for All Bodies, will not be set to Yes as read-only at initialisation, but only if the user tries to change it.

Error/Warning Messages:

- If a solved fatigue result uses an analysis which has be cleared or resolved, the result object will become suppressed or invalid when the user selects it.

- If the geometry selection has a plastic behaviour assigned, a warning message will be displayed


- 12 -

5 References

1. ASME. Section VIII, Division 2. 2017.


- 13 -

This example shows, step by step, how to use the Fatigue (ASME VIII Div.2) result object, as well as verification of the results.

A Static Structural analysis is created and a material with elastic behavior is used. The material properties are summarized in Table 5-1.

Table 5-1: Material Properties of the Duplex Stainless Steel material. Material Property Value

Elastic Modulus [GPa] 185.7

Poisson’s ratio [-] 0.31

The geometry used in this example is a Blind Tee, modeled as a solid multibody part. The previously defined material is assigned to all bodies.

The model is subjected to an internal pressure with its corresponding cap force. Further, the outlet surface is fixed in the axial and tangential direction with respect to a local coordinate system as shown in Figure 5-1. For simplicity, symmetry is utilized such that only half of the geometry model is used.

Figure 5-1: Loads and boundary conditions for the example model

The solved analysis defined the first Load Case and is renamed as Fatigue LC1_BlindT.

The Setup cell of Fatigue LC1_BlindT is duplicated on the Project page (RMB in the Setup cell, duplicate), thus sharing the Engineering Data, Geometry and Model cells, as shown in Figure 5-2. This is done in order for the two analyses to share the same mesh, which is a requirement


- 14 -

to evaluate the cumulated damage from the two analysis. The second analysis is renamed Fatigue LC2_BlindT.

Figure 5-2: Duplicating analysis by duplicating the Setup cell (left) duplicated analysis after renaming (right)

For the Fatigue LC2_BlindT analysis, a Remote Force of 10 000 N is added as shown in Figure 5-3.

Figure 5-3: Loads and boundary conditions for the Fatigue (ASME VIII Div.2) example model.

To evaluate the accumulated damage in the Blind tee, a Fatigue (ASME VIII Div.2) result object is added from the toolbar and scoped to the body. This object is found in the Results drop-down menu of the extension, as seen in Figure 5-4.


- 15 -

Figure 5-4: Inserting a Fatigue (ASME VIII Div.2) object and Details of Fatigue (ASME VIII Div.2) result object.

Load Case Combination is set to Yes. Start Step, End Step and Number Of Cycles fields disappear. Instead, a new field Load Case Table appears as shown in Figure 5-5. By clicking on Tabular Data in the Load Case Table field, a table pops up with properties as shown in Figure 5-6. Refer to 0 if the table does not pop up.

Figure 5-5: Details of Fatigue (ASME VIII Div.2) result object after setting Load Case Combination to Yes.


- 16 -

Figure 5-6: Load Case Table after clicking on Tabular Data.

Two lines are added to the table by clicking twice on . Then, the table is filled in as shown in Figure 5-7: The analysis without Remote Force (here renamed LC1) is selected with 5 500 cycles, and the analysis with Remote Force (here renamed LC2) with 5 000 number of cycles.

Figure 5-7: Load Case Table after inserting two lines, and filling with the values. Note that only solved analyses are valid.

By clicking “Apply” in the Material Table Data field, the property becomes valid as shown in Figure 5-8. Note that, exiting by any other way will not save the table.


- 17 -

Figure 5-8: Details of Fatigue (ASME VIII Div.2) result object after clicking Apply. The Fatigue Curve (App. 3-F) is then specified to 3-F.3. When all properties are filled in, the result object status changes to valid, as shown in Figure 5-9.

Figure 5-9: Details of Fatigue (ASME VIII Div.2) result object after selecting the Fatigue Curve.

The result object is evaluated. The result plot is shown in Figure 5-11. Cycles to Failure and Damage Contribution are displayed in the Load Case Table per load case.

Note that in this case, both LC1 and LC2 could have been set as 2 steps in the same analysis. Then, the same result can be obtained by selecting the relevant start and end steps, as shown in Figure 5-10.

Figure 5-10: Load Case Table for one analysis with two steps, the same damage result is obtained.


- 18 -

Figure 5-11: Plot displayed and Load Case Table after evaluation of the result object. (Maximum damage for LC2 alone is not found at the same location as the maximum cumulated damage for both load cases)


- 19 -

Verification of the result at the Maximum Accumulated Damage node:

To verify the result, the equivalent stresses are extracted at the node of maximum accumulated damage for both analysis, see Figure 5-12. The local thermal stress is not included in the stress amplitude calculations, thus, the stress amplitude 𝑆a can be calculated by Eq. 5.36 and Eq. 5.29 in (1) (𝐾𝑓 = 1 𝑎𝑛𝑑 𝐾𝑒,𝑘 = 1):

𝑆𝑎,LC1 =536.79 MPa

2= 268.4 MPa ; 𝑆𝑎,LC2 =

622.26 MPa

2= 311.1 MPa

The numbers of cycles are then calculated using the Annex 3-F in (1):

𝑁LC1 = 25 259 cycles ; 𝑁LC2 = 14 709 cycles

The accumulated damage is then calculated using equation 5.38 in (1):

𝐷 =5000

25 260+

5500

14 644= 0.198 + 0.376 = 0.572

The ratio obtained by hand calculation is equal to the one obtained with the extension result object Figure 5-11 as per conservative discretization of the fatigue curve in the extension. Results are verified.

Figure 5-12: ANSYS Equivalent Stress at the node of maximum utilization for LC1 and LC2.


- 20 -

1- The fatigue curves are built for the bodies of the geometry selection1. The fatigue curves are built as specified by the Annex 3-F for a stress range 𝑆𝑎 varying in the range defined for each table in (1) with a step of 0.2 MPa. Note that: - The Young’s modulus is retrieved from Engineering Data and used as the modulus

of elasticity of the material 𝐸𝑇 in Eq. 3-F.3 in (1). If 𝐸𝑇 is temperature dependent, it will be interpolated at the user defined temperature.2

- The stress amplitude, 𝑆𝑎, is calculated by Eq. 5.36 and Eq. 5.29 in (1). The local thermal stress ∆SLT,k in (1) is not included in the stress amplitude calculations.

- 𝐾𝑓 is strength reduction factor accounting for local notch or effect of the weld. This

factor is set to 1 by default - 𝐾𝑒,𝑘 is the fatigue penalty factor. This factor is set to 1 by default.

2- For each load case and each element nodes, the equivalent (von-Mises) stress range is

calculated for the specified start and end time. The closest superior stress range from the built corresponding fatigue curved is determined which gives the number of cycles.

3- In the case of load combination, the number of cycles to failure for a set of load cases is calculated by Equation 5-1 and the accumulated damage is calculated Eq. 5.38 in (1)

𝑁𝑡𝑜𝑡 = ( ∑1

𝑁𝑖

𝑙𝑜𝑎𝑑 𝑐𝑎𝑠𝑒𝑠

𝑖=1

)

−1

Equation 5-1

The specified results are calculated at element nodes. For unaveraged display, results are plotted at element nodes. For averaged results, element nodes result are averaged and plot at nodes, results are averaged across bodies. The result value at midside nodes is the average of the two neighbour corner nodes results.

1 If a body used a fatigue curve previously built, this step is skipped and, thus, the file is not written to the solver files directory.

2 If the specified temperature is outside of the range for which the Young’s Modulus has been defined, the Young’s Modulus will not be interpolated, instead, the closest value (minimum or maximum) will be selected.


- 21 -

One issue regarding using results from another analysis system in load case definition tables: When this is used, and that other analysis system is invalidated/rerun, the result object is not immediately invalidated. Only when the result item is clicked once, the result item is invalidated.

Stopping the results evaluation by clicking “Stop Solution” at the ANSYS Workbench Solution Status pop-up window is not possible.

The Display Time is not working correctly in the case that the time specified does not have results stored. To ensure expected results, only select points in time where results are stored. In additions, for some result items the Display Time should not be used at all. This is specified in the Usage chapter for the affected result items.

Faces and edges that have been created as Virtual Topology are not selectable as geometry input.

Duplicating an evaluated result item results in an un-evaluated result item. The duplicate result item needs to be re-evaluated.

Three issues are related to pop-up tables. In the case that Mechanical is open in a display other than the main display, the table may not pop up. In the case that Mechanical is open in the main display, but the Mechanical window is scaled too small, the table may not be visible. The only way to close the table is to click on “Cancel” or “Apply”, clicking on the top-right red cross will not close the table.

When inserting an item under the Setup level (Initial Conditions, Loads or Supports), and then un-loading the extension, the item is not possible to delete afterwards. The extension needs to be reloaded before the item can be deleted.

For result items, the availability to select geometry as mesh elements or nodes is limited.

Some load and result objects refer to Body ID. The Body ID can be found by using Selection

Information in the main toolbar, as shown in Figure 5-13. ID (beta) displayed under definition in the detail view of a body, is not the Body ID.

Figure 5-13: Selection information table.

Documentation, ASMEFatigue Documentation V190

Documents

Transcript of Documentation, ASMEFatigue Documentation V190