# Regarding tensile test simulation

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On 3/12/2016 at 11:30 AM, Abhishek Kumar said:

Ok I just checked RADIOSS Manual. In this model we need to give values of D1,D2 and D3. But at present I don't have theses values for the material which I am simulating.This failure model is based on stress triaxiality and failure strain.For D1,D2 and D3 we need to plot a graph between failure strain and stress triaxiality.

But problem is that I am simulating tensile test simulation to get the value of stress triaxiality for different of specimen under different failure mode. So that I can get the values of stress triaxiality at failure strain.. Then only I can get the value of D1,D2 and D3.

Is there any other method to get the value of stress triaxiality at failure strain?

Thanks and regards,

Abhishek

How to find triaxility?

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Hi Pavan Kumar,

Stress triaxiality is an important and useful character to describe the state of stress, which effects the material damage and fracture.

In /FAIL/JOHNSON card D1, D2, and D3 are constants in the Johnson failure equation that relates plastic failure strain to stress triaxiality.

Please go through the RADIOSS User Guide in Help Menu where this concept is described in /FAIL/JOHNSON card (page 124 onwards).

The following are some common stress states and their triaxiality values:

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Hello Sir,

I had carried out the simulation with specimen having different shape then doge bone specimen. I am unable to get the exact stress strain curve and force vs displacement plot also . I had created the output block with the elements section. I am attaching .hm, .h3d and T01 file with this, please explain me where I am doing mistake.

6.h3d

.T01

6.hm

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Hello Pavan,

From the T01 file select the element for plotting the stress and strain curve. Else, from HyperView also you can plot this using Build Plots menu.

Once these plots are done using cross plot option you can create stress-strain curve.

I'm attaching two documents where cross plotting is shown. Please follow the steps shown in these documents to create a cross plot.

Cross plot values along a specified node path (1).pdf

Cross_Plot.pdf

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Thank you for the reply Sir,

I have already used the cross plot and getting the stress vs strain in one plot. I have also used the T01 file in Hypergraph for plotting this for an specified element. However the trend of the stress strain curve is not appropriate, Therefore I am requesting you please see my .hm file,  h3d and T01 file and explain me is there any mistake in modelling. I am attaching the stress strain curve plotted using cross plot but the trend of the curve is not appropriate. pleas e see the attachment.

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We are working on your query.We will get back to you soon.

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Hello Sir,

Is there any update...

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Please refer attached mp4 file for plotting crossplot  using shared T01 file. Let us know if you have need any further help.

Crossplot.mp4

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Hello Sir,

I already know how to cross plot two plots in single plot. Therefore I have already attached a image file showing cross plot between stress and strain. You can see in cross plot as it was stress vs strain curve the trend of the curve in inappropriate. Therefore I had requested to see my model and to identify the errors made by me on that.

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Hi Pavan,

The curves depends on the material parameters users provide.

In the material card you have provided Eps_max as 0.981. Please recheck whether this is correct. During the simulation the material is failing in the earlier stages itself and so I think you are getting such a curve.

Also you have created an output block for section (/TH/SECTIO) but there is no cross section in the model. Please go through RD-3540: Front Impact Bumper Model using HyperMesh in Help Menu where defining cross section is shown.

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Hello Sir,

Thank you for your valuable suggestion. I have changed the Eps_max from 0.981 to 9.81. However I am getting the same behavior of the curve after changing max plastic strain value. I have defined the output block for set of element at the gauge portion of the specimen and getting the same behavior of curve. Is there any necessity  to define the cross section at the required zone before meshing of the specimen?

Thanks and Regards

Pavan

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Hi Pavan,

The Eps_max is the failure strain value. The user should have the correct value, obtained from experimental testing, for simulating the fracture. As I said before based on the material parameters we get the outputs. Please remove the eps_max and sig_max values from the material and try running.

If you want to plot the normal forces of the elements you need to define a cross section for those elements.

Alternately, you can also go through the Example 11 - Tensile Test in the Help Menu.

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