section 2 solid composites - msc...

Composites Technology Day, February 2012

SECTION 2

Solid Composites

• Traditionally laminated composites are modeled

as shell elements in Nastran

• When a laminate is thick or when the load path

and state of stress in the structure is three

dimensional, solid elements are more

appropriate

s33 interlaminar normal stress (peel stress) and s31 , s32

interlaminar shear stresses are important in the study of

delamination

Shell vs. Solid Composite Elements

SOL 400 Solid Composites

• Solid Composite Elements

– Available in SOL 400

– Composite layup definition directly assigned to solid elements

– Stress recovery for ply stresses and interlaminar stresses

– Supports progressive ply failure analysis

A few solid composites examples

Stringer/Skin

delamination

Bolted Joint Tension and Compression

test coupons

Scarf Repair

Create the 3D Orthotropic Material

1. Create the 3D orthotropic material

• Anisotropic material relationships (from Nastran 2011 Linear

Static Analysis User’s Guide):

• Orthotropic material relationships (from Nastran 2011 Linear

Static Analysis User’s Guide):

• A tape material is defined in the

coordinate system shown:

• Typically n13 is provided in data

sheets. For example n13 = 0.33

• Nastran wants you to enter n31

• Recall that

• n31 = n13 x (E3/E1) = 0.018

A common mistake is to enter the n13

value into this form

Defining the Composite Layup

2. The next step is to define the laminate layup. This process is very

similar to the shell element laminate setup.

• In Patran, click on the composite laminate icon to bring up the form.

Enter the thickness and orientation of each ply

• The ply thickness can be entered either as the actual thickness, or as a

percentage of the total laminate thickness.

• Two ways to specify ply thickness

1) Enter as a percentage of total laminate thickness

2) Enter actual ply thickness

% of laminate thickness

Actual ply thickness

• Tips on entering ply thickness

1) Enter as a percentage of total

laminate thickness

– All percentages must add up to 100

– Nastran run will fail if the percentages do not

add up to 100

Thickness

Direction

CHEXA Element

2) Enter actual ply thickness

– Make sure the ply thicknesses you enter

sum to a total laminate thickness which

equals to the element thickness. Nastran

will not check this for you.

– Behind the scene, Nastran divides the ply

thicknesses by the total laminate thickness

to compute fractions and use them to fit the

plies inside the element in parametric space.

Defining the solid laminate property

3. The last step is to create a solid laminate property and assign it to

solid elements.

• In Patran, click on the Solid property icon.

• Set the option to Laminate.

3. Create a solid laminate property (cont.)

• Specify the material orientation coordinate system

• It is used to define the X, Y, Z directions for the

orthotropic material property defined earlier.

• The default is the basic coordinate system.

• Specify the material orientation coordinate system

– This coordinate system directly defines the local material coordinate

system. No projection is used.

– Positive q direction is defined using the right hand rule about the local z-

Coord 10001

Element coordinate systems plotted

• The element coordinate system option (CORDM = -1) is useful

here if the element coordinate systems are aligned

appropriately as shown below:

Set to -1

3. Create a solid laminate property (cont.)

• Define the thickness direction

• This tells Nastran how you intend to orient the plies

inside the solid elements

• Define the thickness direction

• Also known as layer direction

Element coordinate

system

• Tip: Use the element coordinate system plot to help you

select the thickness direction

SOL 400 Solid Composites

• Nastran entries generated by Patran

Solid Composite Results

• SOL 400 solid composites

results are available in the

MASTER/DBALL, not in the

– Specify MASTER/DBALL in

Patran before the run

– After the run, attach Master

to access the results

Review the .f06 file

• SOL 400 Solid Layered Composites results – Stress and strain results for each ply are provided at 4 integration points

at mid-ply position

Plotting Stresses in Patran

• Patran stress fringe plot

1) Select Result quantity

2) Select which layer

3) Select stress component

• Ply stress fringe plot fills the entire element

Averaged

Un-averaged

Solid Shell Composites

Solid Layered Composites vs. Solid Shell

Composites

• Solid elements tend to be overly stiff in bending.

• Several layers of solid elements through the thickness are

typically required to correctly simulate a structural member

in bending.

• Solid composite elements have this same limitation. Solid

composite elements with this default formulation are called

Solid Layered Composite (or Regular Solid Composite)

elements.

Solid Layered Composites vs. Solid Shell

Composites (Cont.)

• In cases where bending is dominant, and the model does

not have several layers of solid elements through the

thickness, consider using the solid shell formulation.

• In this formulation, assumed strain functions are added to

the elements to make them behave more like shell

elements when loaded in bending.

• Solid composite elements with this formulation are called

Solid Shell Composite elements.

Tip: Solid shell composite elements

are also known as continuum shell

composite elements

Solid Composites Types

• Each layer has 1 integration

• Maximum of 2040 layers per

element

• Defined by PCOMPLS

– INTi = ASTN

– The thickness direction must

be in the element Z direction

One integration point per layer

Solid Shell Composites

• Each layer has 4 integration

points

• Maximum of 510 layers per

element

• Defined by PCOMPLS – INT8=L

or INT20=Q

Solid Layered Composites

Defining Solid Shell Composites

• To specify the solid shell composite element, the user needs to turn on

the assumed strain formulation. This is done by setting the integration

scheme to Assume Strain on the input properties form.

• The thickness direction must be set to Element Z Direction

Solid Shell

Composite

Must be set

to Element Z

• Define the material orientation coordinate system

– The x-axis of the specified coordinate system projects onto the element face

to create the local material x-axis

• Face “normal” to the element Z direction

– The local z-axis is in the thickness direction

– The local y-axis is obtained by the cross product ( local-z local-x )

– Positive q direction is defined using the right hand rule about the local z-axis

– Thickness direction must be set to Element Z direction

– This is very similar to the way MCID is defined for the CQUAD4

Coord 10001

• Nastran entries produced by Patran

Review the .f06

• SOL 400 Solid Shell Composites results – Stress and strain results for each ply are provided at one integration point

at mid-ply position

Plotting Stresses in Patran • Patran stress fringe plot

1) Select Result quantity

2) Select which layer

3) Select stress component

• Ply stress fringe plot fills the entire element

Averaged

Un-averaged

• Enhanced transverse shear distribution

– When modeling shell-like structures with a single layer of solid

elements, the TSHEAR (transverse shear) parameter can be

turned on to obtain a parabolic shear distribution through the

thickness of the shell

Tips – Enhanced Transverse Shear

Tips – Generating Solid composite elements

Sweeping

Meshing

Solids

• Methods for generating solid composite elements

1. If the geometry is hex-meshable, directly mesh the solids

2. If the geometry is not hex-meshable, mesh the solid face with

quads and sweep them into solid elements

3. Laminate Modeler can extrude solid composite elements from a

shell mesh (see next slide)

• Laminate Modeler

– Extrudes shell mesh into solid composite

elements

– Automatically creates PCOMPLS

– Can split laminate into multiple layers of solids

Tips – Generating Solid composite elements

End of Section 2

section 2 solid composites - msc...

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