Homework answers / question archive / MNE 490/591- FEM for Additive Manufacturing                            Fall 2020   Homework 4                                               (100 Points)           Due: Nov

MNE 490/591- FEM for Additive Manufacturing                            Fall 2020   Homework 4                                               (100 Points)           Due: Nov

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MNE 490/591- FEM for Additive Manufacturing                            Fall 2020

 

Homework 4

                                              (100 Points)           Due: Nov. 3 at 3:30pm

Please submit your Abaqus model and result files (.inp & .dat), and your answer report for all questions listed.

 

Problem 1 (15 Points)

List the 9 ordered logical modules in Abaqus/CAE for a complete finite element analysis job and briefly explain them.

 

Follow the instructions below to complete problems 2&3. Write down your answers as specific as possible to all 15 questions in the text. You may refer to the lecture notes and/or Abaqus documentation as necessary for the usage of input files. 

 

Problem 2 (20 Points)

Abaqus utilities and documentation

Abaqus provides various utilities for obtaining information on usage, system configuration, example problems, and environment settings for the analysis package. 

1. Start the CMD window from the working folder, enter the command

abaqus information=system to obtain information on the system.

Note that _abaqus is a generic command that may have been renamed on your system. For example, if more than one version is installed on the system, the command might include the version number, as in _abq2018. In the remainder of this workshop as well as all subsequent workshops, use the appropriate command for your system.

2. Open the online documentation with the command abaqus doc

Or you can open the documentation through the link:

http://help.3ds.com/2018/English/DSSIMULIA_Established/SIMULIA_Establish ed_FrontmatterMap/DSDocAbaqus.htm

Search for the string _DSLOAD to find information on the ?DSLOAD option. You can find information related to the data line syntax in the Abaqus Keywords Reference Guide (use the hyperlink for the ?DSLOAD option, or open the Keywords Guide directly). The online documentation graphical user interface is shown in Figure W1–1.

 

 

(

A

bove is

previous

documentation version.

Or

the

new

version may show below)

 

 

 

Figure W1–1.  Online documentation

 

3. Search for “plate buckling” to find example problems that discuss plate buckling. 

Question W1–1: What is the example problem that fit the search criteria?

4. Search for “Damage and failure of a laminated composite plate”.

In the subtopics of the problem click Input files. The list of input files associated with this problem appears. You can select any input filename from the list; a separate window will open containing that file.

Note: All example problem input files are included in the Abaqus release and can be obtained also using the abaqus fetch utility. In your terminal window, enter

abaqus fetch job=damagefailcomplate_cps4 at the command line prompt. 

5. Use the online documentation to determine the input syntax for some options. 

A keyword line starts with an asterisk (?) followed directly by the keyword option. Parameters and their associated values appear on the keyword line, separated by commas. Many options require data lines, which follow directly after their associated keyword line and contain the data specified in the Abaqus Keywords Reference Guide for each option. Data items are separated by commas. Refer to the discussions of keyword line and data line syntax in Lecture, as necessary.

	Question W1–2:  Write the input you would use to define a node set called
		TOP_NODES that contains previously defined nodes 21, 22, 23, and node set TOP_LEFT. Hint: Use the information on the ?NSET option in the Abaqus Keywords Reference Guide to determine the necessary parameter and data line.  *NSET,
	Question W1–3:	Write the input you would use to define a velocity boundary condition on a node set named NALL using the direct format. The velocity is 7.0 m/s in the 2-direction. Will this option appear in the model data or the history data portion of the input file? Hint: Use the information on the ?BOUNDARY option in the Abaqus Keywords Reference Guide, including the reference to the “Boundary Conditions” Section of the Abaqus Analysis User’s Guide, to determine the appropriate syntax.
	Question W1–4:	Write the input you would use to define the ?BEAM SECTION option for beam elements in element set ELBEAMS referring to a material named STEEL. The beam has a rectangular cross-section with a height of 0.5 m and a width of 0.2 m. Hint: This option requires one data line for the beam section geometric data. Follow the hyperlink to the beam cross-section library and the rectangular section to determine the appropriate data line input. *BEAM SECTION,

Problem 3 (65 Points)

Analyzing a connecting lug

 

 

Figure W1–2.  Sketch of the connecting lug

 

In this workshop you will model the connecting lug shown in Figure W1–2. The lug is welded to a massive structure at one end, so we assume that this end is fixed. The other end contains a hole through which a bolt is placed when the lug is in service. You have to calculate the deflection of the lug when a load of 30kN is applied to the bolt in the −2 direction.

To model this problem, you will use three-dimensional continuum elements and perform a linear analysis with elastic materials. You will model the load transmitted to the lug through the bolt as a uniform pressure load applied to the bottom half of the hole, as shown in Figure W1–2. In this workshop SI units (N, m, and s) will be used.

Creating the input file

1. View the contents of _{w_lug.inp}. The model and history data are incomplete, and no mesh or loading is defined.

Question W1–5: How many steps are there in this analysis? 

2. View the files w_lug_nodes.inp and w_lug_elem.inp. Boundary conditions and loads will be defined using the node and element sets defined in these files.

Question W1–6: What type of elements are used to model the lug? 

3. Edit the input file to set the INPUT parameter on the ?INCLUDE options to read the appropriate node and element data files.
4. Complete the ?MATERIAL option block by defining an elastic material with elastic modulus E = 200 GPa and Poisson’s ratio ? = 0.3. The complete material block should appear as follows:

 

*MATERIAL, NAME=STEEL

*ELASTIC

200E9, 0.3

 

Question W1–7:  Do you need to define a density to complete the material definition? Material density is necessary for what types of analyses?

The boundary conditions and the loads cannot be defined without knowledge of the node

 

and element sets and surfaces. Figure W1

–

3

shows the

various sets and surfaces.

Element set

BUILTIN

Node set LHEND

Surface PRESS

Node set

HOLEBOT

 

Figure W1–3.  Useful sets and surfaces

 

5. Boundary conditions are applied using the ?BOUNDARY option. Use the online documentation to obtain a description of the option. The left end of the lug is fixed. Thus, constrain degrees of freedom 1 through 6 of all nodes in node set _LHEND by entering 

 

*BOUNDARY

LHEND, 1, 6

 

6. Distributed loads are applied to surfaces using the *DSLOAD option. In this problem, the load should be applied to the surface named _PRESS (which covers the bottom region of the hole). The option to specify the distributed (pressure) load on this surface is

 

*DSLOAD

PRESS, P, 50.E6

 

The magnitude of the applied uniform pressure is 50 MPa. We determined the load magnitude by dividing the total load by the projected horizontal area of the

hole, where 3 0 k N = 5 0 M P a .

2 ? 0 .0 1 5 m ? 0 .0 2 m

7. Add printed output requests to the step using the ?NODE PRINT and ?EL PRINT options. Abaqus includes a large amount of printed output by default. Requesting printed output of specific variables allows you to limit the volume of output to the data (_.dat) file. Request printed data output of nodal displacements for node set _HOLEBOT and reaction forces for node set _LHEND (including the total force). In addition, request output for stresses in element set _BUILTIN. 

You can do this by entering

 

*NODE PRINT, NSET=HOLEBOT

U2

*NODE PRINT, NSET=LHEND, TOTAL=YES, SUMMARY=NO

RF

*EL PRINT, ELSET=BUILTIN

S, MISES

 

Default output requests for the output database are made automatically, and they will be sufficient for this workshop.

Submitting a datacheck analysis

1. Submit the job for a datacheck analysis by entering the command

abaqus datacheck job=w_lug interactive

at the prompt. The _interactive parameter will cause all log file output to print to the screen.

2. View the data file (_{w_lug.dat}) in a text editor. 
3. Search for the strings “WARNING” and “ERROR” to find any warning and error messages. These messages will indicate whether anything unusual was encountered during the datacheck analysis (keep in mind that your editor may be case-sensitive for searching).

Question W1–8: What warning messages did you get? Do they require changes to the input file, or can you ignore them?

4. Search for the string “P R O B L E M” to see the summary of the problem size. Include spaces between the letters of the search string.

Question W1–9: How many elements are there in the model?  How many variables are there?

Running a complete analysis

1. Submit _{w_lug.inp} as an Abaqus job in interactive mode by typing

abaqus job=w_lug interactive at the prompt.

If the driver asks if you want to overwrite old job files, type “y.” This means that output files with the same job name that exist from a previous analysis will be overwritten.

2. Now resubmit the job in background mode by typing

abaqus job=w_lug at the prompt.

The log file output will be saved in _{w_lug.log} instead of printing to the screen. You can open _{w_lug.log} in a text editor and view its contents.

3. You can also let the Abaqus driver prompt you for the necessary job information by typing

abaqus  at the prompt.

Specify _{w_lug} at the prompt for the job identifier, enter [RETURN] at the prompt for user subroutines (since there are none for this job), and type “y” to overwrite the files from the last run with the same name. Doing so will submit the analysis job in background mode. 

4. List all files with _{w_lug} as the root of the file name (using a “long” format on Unix systems):

dir w_lug.*             (NT) ls -l w_lug.*        (Unix)

Note the files that were created by Abaqus. We will take a closer look at the printed output file (w_lug.dat) later in this workshop.

Results visualization in Abaqus/Viewer

1. To run Abaqus/Viewer and load the output database for the lug analysis, type

abaqus viewer odb=w_lug at the prompt.

Note: The file name extension (_.odb) is not needed.

If an output database is not specified on the command line, you can select

File→Open from the main menu bar in Abaqus/Viewer to access the Open Database dialog box, as shown in Figure W1–4. Select the file _{w_lug.odb} from the output database list.

 

Figure W1–4.  Open Database dialog box

 

2. When Abaqus/Viewer opens the output database, the undeformed model shape will be displayed. To change the plot mode, you can use either the Plot menu or the toolbox icons displayed on the left side of the viewport (see Figure W1–5). You can identify the function of each tool in the toolbox by positioning your cursor above the icon for that tool. A label for the icon will pop up describing its function.
3. To plot the deformed shape, click the Plot Deformed Shape tool  in the toolbox or select Plot→Deformed Shape from the main menu bar.
4. Open the Common Plot Options dialog box by clicking  in the toolbox. Turn on the node and element numbers, and make the nodes visible.

   5.

   Use the display option tools to switch to hidden line, filled, or wireframe display.

   Figure W1

   –

   5

   .  Abaqus/Viewer main window

   View manipulation tools

   Display option tools

   Toolbox

   Results

   Tree

 

1. 6. Note the displacement magnification factor shown in the bottom of the title.

By default, Abaqus/Viewer automatically scales the displacement according to the maximum model dimensions for a small-displacement analysis. Displacements are scaled so that the deformed shape will be clear. For a large-displacement analysis the scale factor is 1 by default. Set the displacement magnification factor to 1 so that you can see the actual displacement, and redraw the displaced shape plot.

Hint: You will have to use the Common Plot Options dialog box.

1. 7. Create a contour plot of the Mises stress by clicking the Plot Contours on Deformed Shape tool  in the toolbox.
   8. Frequently users want to remove all annotations that are written on the plots, especially when they are creating hard-copy images or animations. From the main menu bar, select Viewport→Viewport Annotation Options to suppress the annotations used in the plots.

The annotations are divided into three categories: legend, title block, and state block. Each category can be controlled separately. The title block contains information about which Abaqus version was used and when the analysis was performed. The state block contains the step title (which is the text provided on the data line of the ?STEP option), the increment and step time of the data being displayed, and information on the variable and magnification factor used to calculate the shape of the model.

1. 9. From the main menu bar, select File→Exit to exit from Abaqus/Viewer.

Viewing the printed output file

Open the printed output file _{w_lug.dat} in the text editor of your choice.

1. Look at the input echo near the top of the file. Below this you will find the section titled “OPTIONS BEING PROCESSED.” This is the first place any warning or error messages will appear.
2. A summary of model data follows. Here you can check that Abaqus has correctly interpreted your model definition.

Question W1–10: Which elements are in element set HOLEIN?

3. Next you will find the summary of history data for each step. Search for the strings “B O U N D A R Y” and “D I S T R I B U T E D” to verify that the boundary conditions and distributed loads have been interpreted correctly. Include spaces between the letters of the search string. To start a search through the entire file, go to the top of the file (some editors will wrap to the top of the file upon reaching the end).
4. The next section in the data file is the results section. The tables are printed according to the various output requests.

Search for the strings “N O D E” and “E L E M E N T” to find the tables that contain the output requested. The maximum deflection and peak stress are reported at the ends of the respective tables. 

Question W1–11: What are the maximum direct stresses in the 1- and 2directions (i.e., _?11 and_?22 )?

(Hint: The maximum direct stresses will occur in element set

BUILTIN.)

Question W1–12: What is the deflection of node 20001 in node set _HOLEBOT in the 2-direction?

5. Search for the string “TOTAL” to find the sum of the reaction forces in the 2direction.

Question W1–13: What is the net reaction force in the 2-direction at the nodes in node set _LHEND? Is this equal to the applied load?

Question W1–14: Is the sum of the reaction forces at the nodes in node set LHEND in the horizontal direction (1-direction) zero? Why?

Modifying the model and understanding changes in the results

1. Open the input file _{w_lug.inp} in the text editor.
2. Reduce the distributed pressure load to 25 MPa.
3. Save the modified file to a new file named _{w_lugmod.inp}.
4. Submit the new input file as an Abaqus job.
5. Look at the output database file in Abaqus/Viewer. 

Question W1–15: What is the deflection of node 20001 in node set _HOLEBOT? Do the results reflect the proportional reduction in loading in a linear analysis?