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Author Topic: Residual stress and strain for composite laminates  (Read 74 times)

garyjh

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Residual stress and strain for composite laminates
« on: November 28, 2017, 04:44:00 AM »
How are residual stress and, in particular, strain for composite laminates determined following cure?

How are they differentiated from mechanical and thermal loading?

Can see CTE's input in the orthotropic material creation & also, what looks like deltaT inputs from reference T and thermal expansion & bending effects in the Laminate Analysis and Effective Laminate Properties. But not clear how the residual strains are calculated, or how added or subtracted from mechanical strains, then MS calculated?

Can the strains be calculated without any mechanical or thermal loading i.e. deltaT is cure temp cool down to room temp? Then deltaT is room temp to operating temp?

Please can you help explain or point me to the relevant help & theory  documentation.

Documentation I can find is:
"HyperSizer_Stiffness_Method_-_Thermoelastic_In-Plane_Stiffness_Formulation.HME.pdf". But this looks like for a stiffened panel. Is there some other basic laminate HME that explains it?

And from help when in Laminate Analysis and Effective Laminate Properties:
"Ref Temperature This is the temperature at which the ply material properties are taken. The default temperature is 72° F.
To add another temperature to the list, type the temperature in the box and press [Enter].
If an effective laminate is created, material properties will be generated for each temperature in this list.
Outer/Midplane/Inner Fiber Delta T Specifies through-thickness changes in temperature at the inner, midplane, and outer fibers. Changes are taken to the reference temperature (above). Given these three temperature points, the final temperature distribution is linearly interpolated through the thickness.
The final temperature at each ply is the temperature at which material properties are taken. The analysis will not compute thermally induced ply stresses and strains. However, if the analysis is done in the Sizing form, thermally induced ply stresses and strains will be captured."

So it looks like it is calculated in the Sizing form? Is the strain breakdown of residual, mech & thermal included in the stress report?

Thanks.
« Last Edit: November 28, 2017, 04:56:55 AM by garyjh »

Stephen

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Re: Residual stress and strain for composite laminates
« Reply #1 on: November 30, 2017, 06:50:58 PM »
If you want to capture the strains due to temperature change post-cure, HyperSizer can handle them in the same way it handles other thermal loading. So in that sense, there is not a fundamental difference between the two.

What you would likely want to do is define an initial temperature in your FEM (this is the cure temperature), as well as the applied temperature (this is the operating temperature). When you use this FEM in HyperSizer, it will automatically apply thermal loads according to the deltaT from initial to applied. Since HyperSizer handles this the same way as other thermal loading, you can calculate strains without applying other loads.

As far as the theory, you did in fact point to the correct HME (here). Similar processes are used for both stiffened panels and laminates. Specifically see Section 4.1 which explains the steps HyperSizer takes to determine the ply-level strains resulting from applied thermal loads.

As a note, if you are using non-FEA projects instead, the same process applies, but you will specify the relevant information (initial and applied temperatures) in HyperSizer rather than in FEA.

Let me know if I can answer other questions or clear anything up.

Thanks,
Stephen