An X–Y data object is a collection of ordered pairs that ABAQUS stores in two columns—an X-column and a Y-column. The Operate on XY Data dialog box allows you to create new X–Y data objects by performing operations on previously saved X–Y data objects. In this tutorial you will create a stress versus strain data object by combining a stress versus time data object with a strain versus time data object. Then, you will plot the stress-strain curve.
The first step in creating the stress-strain curve is to create the stress versus time and the strain versus time data objects from the history output. The data objects will contain data from only the first step of the analysis, where the punch rests on the surface of the foam block and compresses the block under its own weight.
To create the X–Y data objects:
In the Results Tree, double-click the XYData container.
The Create XY Data dialog box appears.
In this dialog box, select ODB history output if it is not already selected and click Continue.
The History Output dialog box appears.
In the History Output dialog box, do the following:
Click the Variables tab.
In the Output Variables field, select Logarithmic strain components: LE22 at Element 1 Int Point 1 in ELSET CENT.
Click the Steps/Frames tab.
Select Step 1.
Click Save As.
The Save XY Data As dialog box appears.
Name the X–Y data Strain, and click OK.
A data object called Strain containing logarithmic strain data (LE22) from integration point 1 of element 1 during the first step of the analysis appears in the XYData container.
Use a similar technique to create a data object containing stress data (S22) from integration point 1 of element 1 during the first step of the analysis. Name this data object Stress.
Now you are ready to combine the two data objects to create a stress versus strain data object.
Dismiss the History Output dialog box.
In this section you will create a stress versus strain data object by combining the stress versus time and strain versus time data objects.
To combine the data objects:
In the Results Tree, double-click the XYData container.
From the Create XY Data dialog box that appears, select Operate on XY data and click Continue.
An Operate on XY Data dialog box appears. The dialog box contains the following lists:
The XY Data field on the left contains a list of existing X–Y data objects.
The Operators field on the right contains a list of all the possible operations you can perform on the data objects.
From the Operators field, click combine(X,X).
combine( ) appears in the expression text field at the top of the dialog box.
In the XY Data field, drag the cursor across both the Strain and the Stress data objects to select both and click Add to Expression near the bottom of the dialog box.
The expression combine("Strain","Stress") appears in the expression text field. In this expression "Strain" will determine the X-values and "Stress" will determine the Y-values in the combined plot.
From the buttons along the bottom of the Operate on XY Data dialog box, click Save As.
From the Save XY Data As dialog box that appears, enter the name Stress/strain and click OK.
The new data object Stress/strain appears in the XY Data Manager.
Cancel the Operate on XY Data dialog box.
You will now use the Stress/strain data object that you just created to plot the stress-strain curve.
To plot the stress-strain curve:
Your plot of stress versus strain will inherit the customized settings from your previous plot. To restore the default plot options, do the following:
In the Results Tree, expand the XYPlots container.
Click mouse button 3 on XYPlot-1; from the menu that appears, select XY Plot Options.
In the XY Plot Options dialog box that appears, click Defaults.
Click Apply.
In the XYData container, select Stress/strain. Click mouse button 3; from the menu that appears, select Plot.
A plot of the stress-strain curve with default axis titles appears in the viewport.
To change the axis titles, click the Titles tab in the XY Plot Options dialog box. Select User-specified for both axis titles, and type Strain for the X-axis title and Stress for the Y-axis title.
Click OK to see your titles and to close the XY Plot Options dialog box.
The plot of stress versus strain appears, as shown in Figure D–14.
