Lab1 Truss

8/14/2019 Lab1 Truss

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AAE 320 - Introduction to PATRAN and ABAQUS

Lab. 1 : Analysis of truss structures with ABAQUS

1. Introduction

ABAQUS is a general purpose finite element code which can solve a large variety of problems, ranging from very

simple (as we will se in this lab) to very complex. The code is developed and commercialized by Hibbit, Karlssonand Sorenson, Inc., located in Pawtucket, RI. ABAQUS has its own mesh generation and visualization capabilities,but in this series of labs, we will use another (more powerful and widely used) commercial code for pre- and post-processing operations, PATRAN (version 3.0), owned by the MacNeal-Schwendler Corporation. PATRAN iscompatible with a series of commercial codes, such as NASTRAN, ABAQUS, ... through a series of interfaces.Unlike the previous versions of PATRAN, these interfaces are run directly from PATRAN itself, so that one does nothave to leave the software to run the analysis program. The objective of these few labs is to illustrate, throughexamples of increasing complexity, the capabilities of PATRAN and ABAQUS.

In this first lab we will focus on ABAQUS by creating an ABAQUS input file for a simple truss problem. During thislab we will learn how to:

-define nodes-generate an element connectivity table-prescribe a material description

-impose displacements-apply nodal loads-generate various output files-perform a simple post-processing analysis using ABAQUS/Post

Unlike most commercial finite element codes, ABAQUS runs all problems only in batch mode. It reads the input filecalled jobname.inp (where jobname is an arbitrary name specified by the user) containing a full description of theproblem, then runs the problem min the background. A message is displayed on the screen when the process iscompleted.

The input file jobname.inp contains a series of input commands (or cards) describing the mesh geometry, the appliedloads, the requested output files, ... Among the various output files created by ABAQUS, the following are the mostimportant.

1) jobname.dat This text file contains all of the details of the execution, and gives a summary of the

results. It also lists error messages if there was an error in running ABAQUS.2) jobname.res This binary result file is used in post-processing by ABAQUS/Post3) jobname.fil This binary file will be used when transferring data from ABAQUS to PATRAN in

future labs.

The following handout will only provide the most basic information regarding ABAQUS. For further details aboutthe commands encountered in the various lab sessions, refer to the ABAQUS manuals, and especially to

ABAQUS/Standard Users Manual : contains most of the useful information regarding the ABAQUScommands, the library of elements supported by ABAQUS, etc. ABAQUS/Post Manual : describes the post-processor ABAQUS/Standard Example Manual ABAQUS/Standard Verification Manual

2. Two-dimensional truss problem

2.1 Problem description

We will solve the simple 2D truss problem illustrated in Figure 1. This elementary truss is used to simulate the rearsection of a typical truss fuselage structure. This type of structure was widely used in the early days of aviation, and itis still in wide use for light aircrafts (especially homebuilt aircrafts).The element cross section area is 0.1 in

2and the elements are made of steel (E=30*10

6psi). The structure is

discretized by 11 nodes and 19 elements. Two point loads are applied at nodes 10 and 11 to simulate the down-load


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produced by the horizontal tail. In addition, imposed (zero) displacements are specified at nodes 1 and 2, as indicatedin Figure 1.

2.2 Input file truss.inp

Using your favorite editor, create a file called truss.inp, containing the following series of instructions. While youare entering the data cards, follow the comments listed in Section 2.3. Note that it is essential that you enter the dataAS SHOWN, since ABAQUS is often case-sensitive. Note also that you do not really need to introduce the cards

starting with a double asterisk ** since these are comment lines which are ignored by ABAQUS.

**List of input data cards for a simple 2D truss problem*HEADINGTRUSS PROBLEM 1**First introduce the nodal positions.*NODE, NSET=NODES11,0.0,0.02,25.0,0.03,50.0,2.54,75.0,5.05,100.0,7.56,125.0,10.0

7,25.0,20.08,50.0,20.09,75.0,20.010,100.0,20.011,125.0,20.0**Then the connectivity table (i.e., the list of elements) is introduced.*ELEMENT, TYPE=T2D2, ELSET=TRUSS1,1,22,2,33,3,44,4,55,5,66,1,77,2,78,2,89,3,810,3,911,4,912,4,1013,5,1014,5,1115,6,1116,7,817,8,918,9,1019,10,11**Next we enter the material description.*SOLID SECTION, ELSET=TRUSS, MATERIAL=STEEL0.1*MATERIAL, NAME=STEEL*ELASTIC30.0E6**Next we impose the boundary conditions*BOUNDARY1,1,22,2**Type of analysis and load description*STEP, PERTURBATION*STATIC


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*CLOAD10,2,-20011,2,-220**Finally, specify the content of the output files*EL PRINT,SUMMARY=YESS11,E11*EL FILE,ELSET=TRUSSS,E*NODE FILE,NSET=NODES1

U,CF,RF*RESTART, WRITE*END STEP

2.3 Description of the input file

This section describes the instructions contained in the input file listed in the previous section. The numbers inparentheses indicate section numbers in the ABAQUS/Standard Users Manual where additional information about thecommands can be found.

Lines starting with a single asterisk * are command lines. They MUST BE in all CAPS.Lines starting with a double asterisk ** are comment lines. They are not executed.

*HEADING (8.1.1)Tells ABAQUS that the next line contains the title of the analysis.

TRUSS PROBLEM 1This is the title of the analysis.

*NODE, NSET=NODES1 (8.2.7)The *NODE command tells ABAQUS that nodal coordinates will follow. The NSET=NODES1 tells

ABAQUS that all of the following nodes will be grouped together in a node set called NODES1. The name isarbitrary (it could have been called DOG). It is not necessary to use node sets, but it can be helpful for referring tonodes in later ABAQUS commands. For example, we could have grouped the top nodes (in NSET=TOPNODES)and the bottom nodes (in NSET=BOTNODES).

To enter node data, either all of the nodes information must be explicitly entered, or a command must beused to invoke the automatic node generation routine within ABAQUS. In this lab, all of the nodes will be enteredexplicitly. The first number is the node number followed by its x,y,z coordinates. If no value is given, it is assumedto be zero. For example to enter the point (2,0,4) at node 17, the following lines are equivalent:

17,2.,0.,4.17,2.,,4.

*ELEMENT, TYPE=T2D2, ELSET=TRUSS (8.3.2)The *ELEMENT command tells ABAQUS that element data is to be listed next.The TYPE command is needed to tell ABAQUS what type of element is used. The list of available element

types can be found in Chapter 3 of the Users Manual. T2D2 indicates a 2D truss element with 2 degrees of freedomper node (U and V displacements). This particular element is described in detail is Section 3.5.2.

The ELSET command is the same as the NSET command. All of the elements listed below will bemembers of element set TRUSS. Again, the name is arbitrary and the use of ELSETs is optional.

To enter the element data, either all of the nodes must be explicitly entered, or a command must be used toinvoke the automatic element generation routine within ABAQUS. Again, we will enter the element data explicitlyfor this lab. The first number is the element number followed by the list of nodes that make up that particularelement. In the case of the 2 node truss elements, the node numbering is not important. For example 1,1,2 and 1,2,1would represent the same element, with the angle of reference 180 degrees off of each other. In quadrilateral elementsand other 2D and 3D elements, the node numbering is important.

*SOLID SECTION, ELSET=TRUSS, MATERIAL=STEEL(8.4.19)


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The third chapter of the ABAQUS Users Manual lists the property data needed to describe each element. Asdescribed in (3.5.2), a truss element such as C1D2

1requires only the *SOLID SECTION card, which is followed by

the cross sectional area of the bars.The command *SOLID SECTION, ELSET=TRUSS, MATERIAL=STEEL means that all the elements

belonging to the set ELSET=TRUSS have MATERIAL=STEEL with an area (the next line is the cross sectionalarea) of 0.1 in

2. If there had been two different materials, there would be two *SOLID SECTION lines.

The MATERIAL=STEEL command refers the elements to material property information. The nameSTEEL is again arbitrary. ABAQUS does not interpret the names, just the links between them. As you may havefigured out by now, we are building a data tree of information. The elements are linked to element data which is

linked to material information.

*MATERIAL, NAME=STEEL (8.9.2)For each MATERIAL, various properties need to be introduced. For example, the *ELASTIC (8.9.18)

means that the MATERIAL with NAME=STEEL is linearly elastic. Following the Elastic card, Youngs modulusand Poissons ratio are needed. (The latter is not actually needed in this truss problem, and if not entered will beassumed to be zero).

*BOUNDARY (8.11.2)The *BOUNDARY card tell ABAQUS where the constrained degrees of freedom are located. ABAQUS uses

the standard notation for degrees of freedom:

DOF# Description1 U (disp. in X-direction)

2 V (disp. in Y-direction)3 W (disp. in Z-direction)4 x (rotation about X-axis)5 y (rotation about Y-axis)6 z (rotation about Z-axis)

For a general 3D truss problem, only degrees of freedom #1, 2 and 3 are considered. In this 2D example, only DOF#1 and 2 will be used. The rotation degrees of freedom will show up in beam bending, plate and shell problems.

To constrain a degree of freedom at a node, list the node number followed by the number of the degree of freedom to beconstrained. For example: 3,1,2 means that node 3 is constrained in DOF #1 and 2 (U and V displacements). SeeSection 10.4.1 of the Users Manual if non-zero nodal displacements are to be imposed.

Note: ONLY two degrees of freedom can be constrained per line. To fix U, V, and W displacements in a 3D problemit is necessary to use two lines, or to invoke the PINNED command as follows:

1,PINNEDThis tells ABAQUS that node 1 is constrained in U, V, and W displacements.

*STEP, PERTURBATION (10.1.1)Various types of loading can be introduced in ABAQUS. The simplest one, the *STEP,PERTURBATION,

means that the loading case will be just a simple step, turned on once. The loading can also be entered as a set oftime coordinates with loading conditions so that gradual loads can be applied instead of a simple step. See chapter 10on AMPLITUDE discussion for more information. The PERTURBATION command tells ABAQUS that only thelinear step will be considered and no nonlinear analysis will be performed.

*STATIC (10.2.13)The *STATIC card tells ABAQUS that static loading will be applied (as opposed to dynamic or other types

of loadings.).

*CLOAD (10.3.5)CLOAD stands for concentrated loads. This is a load applied at a node. DLOAD (distributed load) can also

be used. To use CLOAD, list the node number followed by the degree of freedom and the load value. If the load isapplied at an angle, it must be broken up into components and introduced as two entries (if the load is in a plane) orthree (if the load is applied in a space). For example, 5,2,-7500. means that at node 5 in the Y direction there is aload of 7500 (in the negative Y-direction).

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The element T2D2 is referred to as C1D2 in the older versions of ABAQUS.


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*EL PRINT,SUMMARY=YES (10.11.3)*EL PRINT means that element data will be printed in the result file called jobname.dat with a summary of

the max and min values. Following the card is a list of the data that is requested. In this particular case, we are onlyinterested in

the axial stress S11the axial strain E11

As mentioned earlier, the description of all the elements available in the ABAQUS element library is given in chapter

3 of the ABAQUS/Standard Users Manual. This chapter also contains the list of element values that are associatedwith each element and that can be exported for post-processing. For more information, consult the section ElementOutput associated with each element described in Chapter 3.

*EL FILE,ELSET=TRUSS (10.12.3)*EL FILE tells ABAQUS to create an element file for conversion to other post-processing codes. It will

make an element file that can be used with PATRAN. ELSET=TRUSS refers to all of the elements that will be inthe element file. The ELSET command is optional : if absent, the values for all the elements will be written in thefile for further post-processing. In this first lab, we will not use this particular file since we will be usingABAQUS/Post for the post-processor. Depending on the type of analysis and the elements used, there are a series ofelement values available for output. Each quantity is denoted by an identifier. See Section 10.10.2 in the UsersManual for the list of available element quantities. For example,

S,E indicates that all stresses and strains will be listed in the output.

*NODE FILE,NSET=NODES1 (10.12.7)*NODE FILE is the same as EL FILE except:

Depending on the problem, there is a series of nodal values available for output. Each quantity is denoted by anidentifier. See Section 10.10.2 in the Users Manual for the list of available nodal quantities. For example,

U corresponds to the displacementsCF denotes the applied concentrated forcesRF denotes the applied reaction forces

*RESTART, WRITE (8.14.1)This command tells ABAQUS to write a jobname.res file that will be used in post-processing with

ABAQUS/Post.

*END STEP (10.1.2)This ends ABAQUS processing.

2.4 Running ABAQUS

To run ABAQUS, simply enter the command:

abaqus job=truss (since we chose truss as our jobname in this case)

ABAQUS will run in the background and will possibly alert you when finished. To make sure that the process isfinished, enter ps to list the active processes : typically, the processes initiated by ABAQUS are jobname.com andstandard.x. If none of these processes appear in the list of active processes, the run must be over.To view the results, look at the truss.dat file. If there were run time errors, they will be reported in this file. Take afew minutes reviewing the content of this file.

3. Post-Processing with ABAQUS/Post

In this section, we describe how to perform a simple post-processing using ABAQUS/Post, which is run interactivelyon an X-Window terminal by entering

abaqus post restart=truss (since the results needed for ABAQUS/Post are in the truss.res file)

It is not the objective of this session to introduce the extended capabilities of the ABAQUS/Post post-processor. Wewill limit ourselves to the basic commands required to visualize the mesh (deformed and undeformed) and the stressand strain values in the various elements.


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First a list of some basic commands which are useful in ABAQUS/Post (Note: ABAQUS/Post is case-insensitive)

SET, N NUMBERS=ON (OFF) turns on (off) the node numbersSET, EL NUMBERS=ON (OFF) turns on (off) the element numbersSET, N SIZE=0.003 Plots dots at the node locationsSET, BC DISPLAY=ON (OFF) turns on (off) the display of applied b.c.SET, LOAD DISPLAY=ON (OFF) turns on (off) the display of the applied loads

To draw the undeformed mesh, simply type:

DRAW

To draw the deformed mesh, type:DRAW, DISPLACED

You should get something similar to Figure 2. Note that the displacements are greatly amplified (the magnificationfactor is given by the legend at the bottom of the screen).

To draw the stresses (strains) type:CONTOUR, VARIABLE=S11 (E11)

The three mouse buttons (if properly initialized) can be used to-rotate the mesh (left button)-translate the mesh (center button)-zoom (right button)

You can also zoom in on a chosen are by typing:ZOOM, CURSOR

Then pick a window with the mouse. Then redraw your previous plot (you can use the arrow keys to move up anddown the stack of previous commands). To restore the full original window type :

ZOOM, RESET

Any of the ABAQUS/Post commands can be abbreviated as long as they are still not ambiguous. Excellent help isavailable by typing ? at any time. You can also obtain the description of a particular command (say CONTOUR)by entering:

HELP, CONTOUR

To quit ABAQUS/Post enter:END

How to obtain a hard copy of a plot?

When you want to obtain a hardcopy of a plot that you have on the screen, type:SET, HARD COPY

to turn on the hard copy output. All output will be stored in a file called jobname.mpl. Redraw the plot you wanta hard copy of . To turn off the hard copy output, enter once again:

SET, HARD COPY

To create a postscript file from the jobname.mpl file type:abaqus plot job=truss device=cps

This will generate a postscript file called jobname.ps. A few questions will be asked on the screen. One can changethe default answers or just hit enter until it stops asking questions.

After ABAQUS/Plot is completed, a postscript file will be created and can be printed (using the lpr or the lpcommand depending on the machine you are working on).

4. EXCERCISE

Now that you have performed an analysis on a 2D truss, it is time to move on to a 3D truss structure. To save time,an incomplete input file named truss3d.inp is provided. All that is necessary is to insert the appropriate informationand run the analysis. As before, the structure is a simple fuselage structure but now it is expanded to 3D (Figure 3).Listed below are tables showing the required boundary conditions and loads at the specified nodes. For the materialproperties use steel (E=30.0*10

6).


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Node # Fixed Displacements1 u,v,w13 u,v,w7 u,v,w18 u,v,w

Node # Direction of LoadApplied load

11 w -100

12 w -20022 w -10012 u 756 u -75

** List of input data cards for a 3D truss*HEADING3D TRUSS PROBLEM** First introduce the nodal positions*NODE, NSET=NODES11,12.0,0.0,0.02,12.0,25.0,0.03,9.0,50.0,2.54,6.0,75.0,5.05,3.0,100.0,7.56,0.0,125.0,10.07,12.0,0.0,20.08,12.0,25.0,20.09,9.0,50.0,20.010,6.0,75.0,20.011,3.0,100.0,20.012,0.0,125.0,20.013,-12.0,0.0,0.014,-12.0,25.0,0.015,-9.0,50.0,2.516,-6.0,75.0,5.017,-3.0,100.0,7.518,-12.0,0.0,20.019,-12.0,25.0,20.020,-9.0,50.0,20.021,-6.0,75.0,20.022,-3.0,100.0,20.0** Then introduce the connectivity table*ELEMENT, TYPE=T3D2, ELSET=TRUSS3D1,1,22,2,33,3,44,4,55,5,66,1,7

7,1,88,2,89,2,910,3,911,3,1012,4,1013,4,1114,5,1115,5,1216,6,1217,7,818,8,9


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19,9,1020,10,1121,11,1222,13,1423,14,1524,15,1625,16,1726,17,627,13,18

28,13,1929,14,1930,14,2031,15,2032,15,2133,16,2134,16,2235,17,2236,17,1237,18,1938,19,2039,20,2140,21,2241,22,12

42,1,1343,1,1444,2,1445,2,1546,3,1547,3,1648,4,1649,4,1750,5,1751,7,1852,7,1953,8,1954,8,2055,9,2056,9,2157,10,2158,10,2259,11,2260,1,1861,2,1962,3,2063,4,2164,5,22** You will be required to complete the following sections of the input file before submitting for analysis.**** Next enter the material description**** Next, we impose the boundary conditions (ie: fixed displacements)**** Type of analysis and load description**** Finally specify the content of the output files

The final deformed shape should look like that presented in Figure 4.

Lab1 Truss

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Transcript of Lab1 Truss