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Author Topic: Correction factor for composite laminates on honeycomb core  (Read 8458 times)

HyperSizer User

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Correction factor for composite laminates on honeycomb core
« on: August 25, 2008, 08:54:32 AM »
I am sizing a panel in HyperSizer. This panel is a sandwich structure, contains a honeycomb core and carbon fiber laminate face sheets. Because of a “pillowing” effect of composite skins in the honeycomb cells during curing, the strength of the skin is typically lower than a monolithic laminates. Therefore a correction factor will be applied for strength of the face sheets/skin materials in a honeycomb structure, while calculating MOS for the ply strength. Does HyperSizer already include this knockdown factor while calculating MOS in the failure tab?

Phil

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Re: Correction factor for composite laminates on honeycomb core
« Reply #1 on: August 25, 2008, 08:56:00 AM »
We have a Laminate "co-cure" correction factor which can be accessed from the Options tab of the Orthotropic material form.  This form allows you to put in correction factors for laminates that are cured on the tool or on a range of different cell size honeycombs.  The correction factors are material dependent, so you can enter different factors for each material. The correction factors can be entered for all of the stiffness terms as well as compressive and tensile strength.  For the compressive and tensile strength, you can enter the correction factors as bi-linear functions of the laminate thickness.
 
Once you have defined these correction factors, they will automatically be applied during the composite analyses as direct multipliers on the allowable properties.  The code will detect the laminate thickness and core diameter and automatically determine the appropriate correction factor.
 

Rocketman007

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Re: Correction factor for composite laminates on honeycomb core
« Reply #2 on: May 26, 2009, 10:26:36 AM »
A Clarification

The user must specify a different material ID (MAT8) for co-cured laminates. In the FEM the user will set up MAT8 properties for the co-cured and pre-cured laminates:

MAT8 (ID1) for co-cured laminates (Note - Hypersizer only reads the MAt8 ID, not the properties on the Nastran card.

and MAT8 (ID2) for pre-cured laminates

The basic lamina material properties will be the same in HyperSizer for both of the above materials  but in the material orthotropic form the user will select OPTIONS/ Correction factors for the co-cured material. The co-cure correction will only be applied to the co-cured laminate.

 Correction factors can be applied to stress, strain and stiffness. Note there will be a stiffness reduction for co-cured laminates in some cases. Correction factors are only applicable with lamina properties.

If using LAMINATE analysis and laminate allowables in HyperSizer, the user needs to set up material properties for the co-cured and pre-cured laminates.

WH

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Re: Correction factor for composite laminates on honeycomb core
« Reply #3 on: May 29, 2009, 07:36:18 AM »
Any guidelines to the input of these correction and co-cure correction factors??



Rocketman007

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Re: Correction factor for composite laminates on honeycomb core
« Reply #4 on: June 25, 2009, 11:29:58 AM »
In the orthotropic form click on options and correction factors. Then click on the property to edit (Ec1) and the EDIT button for co-cured.

These corrections for co-cured laminates are with reference to the baseline pre-cured properties. We enter the same LAMINA properties for our co-cured and pre-cured laminates, but we apply corrections for the co-cured laminates. All pre-cured laminates default to correction factors = 1.0

Co-cured corrections will be determined by test. We compare the pre-cured properties with the co-cured properties. Hypersizer provides several methods for including a co-cure correction factor, from a constant to a bi linear equation based on thickness. A thinner laminate will have a larger co-cure correction factor (lower allowable).

In theory all lamina mechanical properties can have correction factors applied. Each organization must determine preferences. Primarily the compression allowable and stiffness properties can be significantly reduced from the golf ball dimpling effect produced in the laminate from a  co-cured process on a honeycomb core.