COMposite POST - Letecký ústavmalis/compost/compostEN_2.pdf · ABAQUS, NX Nastran can be ... restrictions for composite modeling, ... Recommended way to define the PCOMPG is a laminate

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COMposite

POSTprocessor

v 1.45

COMPOST v1.45 USER GUIDE

(c) IAE FME BUT 2012

2

Compost v1.45 user guide

Table of contents

1 Compost overview ............................................................................................................................ 3

1.1 About .................................................................................................................................... 3 1.2 Purpose ................................................................................................................................. 3 1.3 License ................................................................................................................................. 4 1.4 Installation requirements ...................................................................................................... 4

2 NASTRAN modeling guidelines ...................................................................................................... 5

2.1.1 Supported element types ........................................................................................... 5 2.1.2 Coordinate systems ................................................................................................... 5 2.1.3 PCOMPG .................................................................................................................. 6 2.1.4 Material definition .................................................................................................... 6

3 Using the COMPOST ....................................................................................................................... 6

3.1 NON-GUI ............................................................................................................................. 6 3.2 GUI ....................................................................................................................................... 6

3.2.1 Main window for linear FEM analysis ..................................................................... 6 3.2.2 Select subcases window ............................................................................................ 8

3.2.3 Main window for nonlinear analysis ........................................................................ 9 3.2.4 Options window ...................................................................................................... 10

3.3 Analysis modes ................................................................................................................... 11 3.3.1 Laminate ................................................................................................................. 11 3.3.2 Sandwich Isotropic ................................................................................................. 11

3.3.3 Sandwich Honeycomb ............................................................................................ 12 3.4 Operational modes .............................................................................................................. 13

3.4.1 Report ..................................................................................................................... 13 3.4.2 Analysis .................................................................................................................. 14

3.4.3 Min/Max ................................................................................................................. 15 4 Theoretical background ................................................................................................................... 16

4.1 Failure indices .................................................................................................................... 16 4.2 General notation ................................................................................................................. 16 4.3 Laminate failures ................................................................................................................ 17

4.3.1 Max stress ............................................................................................................... 17 4.3.2 Tsai Wu ................................................................................................................... 17

4.3.3 Tsai Hill .................................................................................................................. 18 4.3.4 Hashin ..................................................................................................................... 19

4.4 Failures of a sandwich with an isotropic core .................................................................... 20 4.4.1 Wrinkling ................................................................................................................ 20 4.4.2 Flexural core crushing ............................................................................................ 21

4.4.3 Shear crimpling....................................................................................................... 22 4.4.4 Core shear failure .................................................................................................... 22

4.5 Failures of a sandwich with a honeycomb core ................................................................. 23 4.5.1 Wrinkling ................................................................................................................ 23 4.5.2 Dimpling ................................................................................................................. 23

5 Acknowledgments ........................................................................................................................... 25 6 APPENDIX ..................................................................................................................................... 25

6.1 Reporting bugs ................................................................................................................... 25 7 References: ...................................................................................................................................... 25

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1 Compost overview

1.1 About

The word COMPOST is an abbreviation of COMposite POSTprocessor. The COMPOST software

is a post processor for finite element solvers. The software is suitable for post processing of finite

element analysis of structures made from composite materials and sandwich structures in early state

of a design.

The COMPOST is written in Python 2.7 language, therefore it is easily to modify and extend by the

user. It was tested on linux and windows machines. Also self installing compiled version for

windows machines is available.

In this current version (r 1.45) only MSC.NASTRAN solver is supported, however support for

ABACUS and MSC.MARC is planned.

You can download the COMPOST from its homepage:

lu.fme.vutbr.cz/~schor/compost.html

COMPOST was written as a part of KOMPROKOM research project by:

Michal Mališ - Project Leader

Petr Špaček - Main programmer

Lukáš Jeza - GUI programmer

Pavel Schoř - Mathematical programmer

1.2 Purpose

The finite element method solver provides complete information about stresses in a given structure.

At the early phase of design complex information about element is necessary (complex stress state

in all layers, applications more than one ply failure criteria). Unfortunately the most commercial

finite element software does not provide evaluation using sandwich structure failure criteria which

consider element as a substructure consist from three layers (two skins and one core).

Therefore the COMPOST software was developed to supply that information to the designer in

easiest way.

The COMPOST consist three main tools for evaluation of structure: Report, Analysis and Min/Max.

Report: printing of main information about structure on one finite element

- Material type, ply orientation, plies thickness

- Result stresses in each plies calculated by finite element analyze (three normal stress and

two through thickness shear stresses)

- Righting the report using html format above mentioned information and plot graphs with

normal and shear stresses in all layers on selected element.

Analysis: printing of main information about structure on one finite element, and calculation

additional results according type of structure. The function applies another three conventional

failure criteria (Max. Stress, Tsai-Wu, Tsai-Hill). In case of sandwich structure the COMPOST

applies sandwich failure criteria on selected elements (wrinkling, dimpling, crimping, core shear

strength, crushing).

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- Printing of material type, ply orientation, plies thickness

- Printing of result stresses in each plies calculated by finite element analyze (three normal

stress and two through thickness shear stresses)

- Application of three failure criteria for solid laminates and in case of sandwich structure

application of sandwich failure criteria.

- Righting the report using html format above mentioned information and plot graphs with

normal and shear stresses in all layers on selected element.

Min/Max: This function is suitable for searching of elements where failure criterion reached the

critical value. The COMPOST applies solid laminate failure criteria and sandwich criteria, if it is

required, on selected elements and returns list of the most critical elements sorted according the

magnitude.

In this current version (r 1.35) only MSC.NASTRAN solver is supported, however support for

ABAQUS, NX Nastran can be consider according demand. (Please contact [email protected])

1.3 License

This program is free software: you can redistribute it and/or modify it under the terms of the GNU

General Public License as published by the Free Software Foundation, either version 3 of the

License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;

without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR

PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If

not, see <http://www.gnu.org/licenses/>.

1.4 Installation requirements

COMPOST requires several software libraries to run. Please download and install all libraries

before you run COMPOST first time.

Python version 2.7

Homepage: http://www.python.org/

Download page: http://www.python.org/download/releases/2.7.3

Installer for Windows x32: http://www.python.org/ftp/python/2.7.3/python-2.7.3.msi

NumPy version 1.6.2

Homepage: http://numpy.org/

Download page: http://scipy.org/Download

Installer for Windows x32: http://sourceforge.net/projects/numpy/files/NumPy/1.6.2/numpy-1.6.2-

win32-superpack-python2.7.exe/download

Matplotlib version 1.2.0

Homepage: http://matplotlib.org/

Download page: https://github.com/matplotlib/matplotlib/downloads

Installer for Windows x32: https://github.com/downloads/matplotlib/matplotlib/matplotlib-

1.2.0.win32-py2.7.exe

PyQt4 version 4.9.5

https://github.com/downloads/matplotlib/matplotlib/matplotlib-1.2.0.win32-py2.7.exe

https://github.com/downloads/matplotlib/matplotlib/matplotlib-1.2.0.win32-py2.7.exe

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Homepage: http://www.riverbankcomputing.co.uk/software/pyqt

Download page: http://www.riverbankcomputing.co.uk/software/pyqt/download

Installer for Windows x32: http://sourceforge.net/projects/pyqt/files/PyQt4/PyQt-4.9.5/PyQt-Py2.7-

x86-gpl-4.9.5-1.exe

(Minimal installation is enough)

2 NASTRAN modeling guidelines

There are a lot of possibilities to solve the problem of composite structures; therefore there are some

restrictions for composite modeling, which are mentioned in this chapter. Following these

restrictions is necessary to proper post processing with COMPOST software.

2.1.1 Supported element types

The COMPOST is based on classical laminate theory; therefore only 2D shell elements are possible

to post-process.

Possible element types in MSC.NASTRAN:

QUAD4

QUAD8

TRIA3

TRIA6

2.1.2 Coordinate systems

Coordinate system serves to define orientation of the composite element in the model space.

Notation is used for composite elements is same as defined in NASTRAN manual [4]:

Figure 1: Coordinate system definition

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2.1.3 PCOMPG

The PCOMPG is used to define a material type, thickness, orientation and stacking sequence of the

laminated material shell property. The Compost software is primarily for post processing of

laminated structures; therefore PCOMPG card is only MSC.Nastran property definition used by

COMPOST software. Recommended way to define the PCOMPG is a laminate modeler in

MSC.PATRAN.

The PCOMPG entry must follow following rules:

Layers have to be numbered in ascending order

Layer materials are limited to linear isotropic MAT1 or linear orthotropic MAT8 only

Please refer to the MSC.NASTRAN user guide [4] for more details about the PCOMPG.

2.1.4 Material definition

Material definition MAT1 and MAT8 are only types enabled for COMPOST software. It is

necessary to fill all material characteristic regarding stiffness, select failure criteria and fill all

failure material characteristics. The density and thermal expansion coefficients are not necessary.

3 Using the COMPOST

3.1 NON-GUI

To solve large tasks the COMPOST can be run on clusters, where there is usually no graphical

interface available. Therefore it is possible to run the COMPOST as a console application. Example

is included in your COMPOST distribution under compost-txt.py

3.2 GUI

Graphical User Interface version act as usual desktop application and user should have no problem

with using this version; however there are some differences, which are explained in this section

3.2.1 Main window for linear FEM analysis

The main window consists of several input dialogs to load necessary files and defines all required

properties. Figure 1 provides description of the main window with explanations in the text bellow.

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1. Settings button – opens settings window, explained bellow

2. FEM solver selector – select supported FEM results to post-process. Currently only

MSC.NASTRAN is supported.

3. bdf input – select input bulk data file for NASTRAN

4. f06 input – select result file from NASTRAN

5. Operational mode – select one of operational modes: Report, Analysis, Max/Min,

Optimization. Currently the optimization is not supported.

6. Element type – select type of element used in the bdf : Laminate, Sandwich with isotropic

core, Sandwich with honeycomb core. Switching the element type will change the user

constants in (8.)

7. Selection of subcases and load step – select one or more subcases from the f06 file. The line

7 depends on type of FEM analysis linear/nonlinear. Explained bellow in chapter 3.2.2.

8. User constants - Provide necessary constants, which are required for analysis. This section

varies in dependence on element type (6.)

9. Element selection – write elements to post-process.

10. Save Files – select folder, where results will be saved. Warning: The COMPOST can create

Figure 2: The main window for linear FEM analysis

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a lot of report files, so select the result folder carefully.

11. Calculation button – start the post-processing. At the end of post-processing, results are

stored in folder selected by (10.) and several result should open in users web-browser.

12. Exit button – exit the COMPOST program

3.2.2 Select subcases window

If more than one subcase is found in the f06 file, the Select sub cases button (7.) appears. By

clicking on it, the user is able to select sub-cases of his interest.

Figure 3: Select subcase window

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3.2.3 Main window for nonlinear analysis

The differences between main window for linear and nonlinear FEM analysis are only in line 7

according figure 1. The COMOST software can recognize the type of simulation according “bdf”

input file and changes the main window. The COMPOST works only for one subcase of nonlinear

analysis. Also exact load step which was reached during the calculation has to be defined. The load

step definition is real number in interval 0 – 1.

Figure 4: The main window for nonlinear FEM

analysis

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3.2.4 Options window

This window allows user to adjust several properties of graphical outputs and maximum number of

reports, which should be opened in the user’s web browser.

Number of reports to open – select number of reports, which should be opened in the web-

browser.

Units on axis x,y – since the NASTRAN is dimensionless, units in graphs are to be given by

the user.

Minimal core thickness – the COPOST differentiates between laminates and sandwiches by

maximum layer thickness found on the element. Specify threshold for this.

Figure 5: Option window

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3.3 Analysis modes

Switching the analysis mode will change some input boxes in the main widow. Following section

will provide you necessary information how to setup analysis parameters correctly.

3.3.1 Laminate

In laminate type mode, only inter laminar stress allowable is given.

3.3.2 Sandwich Isotropic

Figure 6: Option window

Figure 7: Sandwich structure option window

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Inter-laminar stress – set the inter-laminar stress allowable

Wrinkling factor K1 – set the wrinkling constant K1 as described in chapter 4.4.1.

Core strength – set the thought thickness core strength as described in chapter 4.4.2.

Core shear allowable – set the core shear strength as described in chapter 4.4.4.

Core shear correction factor – set the core shear correction factor as described in chapter

4.4.4.

3.3.3 Sandwich Honeycomb

Cell size – set actual honeycomb cell size as described in chapter 4.5.2

Inter-laminar stress allowable

Wrinkling modul Ec – set the core through thickness Young modulus

Wrinkling factor K2 – set the wrinkling constant K2 as described in chapter 4.5.1

Core strength – set the thought thickness core strength as described in chapter 4.4.2.

Core shear allowable – set the core shear strength allowable

Core shear correction factor – set the core shear correction factor as described in chapter

4.4.4.

Figure 8: Sandwich structure with honeycomb core option window

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3.4 Operational modes

The COMPOST offers three different modes of operation. Switching of operating mode will not

change any input box in the main window.

3.4.1 Report

This mode will read NASTRAN result files and will report stresses from these files without any

calculation for post-processing. Typical result is shown bellow

Figure 9: Example of report results

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3.4.2 Analysis

This mode will do the analysis for all selected element. Type of analysis depends on selected

analysis mode. There are three analysis modes available:

Laminate for laminated structures

Sandwich iso for sandwich structures with isotropic core

Sandwich honey for sandwich structures with honeycomb core

Switching the analysis mode will also change some input boxes in the main widow. Typical result is

shown on figure 10.

Figure 10: Example of analysis results

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3.4.3 Min/Max

This mode will read NASTRAN result files, will report stresses and will do the analysis for all

selected elements. From these elements a table with 20 the most critical failed elements is produced.

The failed elements are sorted according the failure with the highest Failure Indices value. Also

critical failure type is displayed. If the number of failure elements is higher than 20, COMPOST

automatically generates external text file with number of all failed elements. (Failed elements

means that at least one FI from all calculated for one element exceed 1.

Typical result report is shown on figure11.

Subcase ID: 1

Processed elements: 426

Failed elements: 17

Element ID Layer Failure type Value

16523 1001 wrinkling-top 1.933






16520 1001 core-shear 1.311








16522 1001 core-shear 1.048

16512 1001 core-shear 1.006


Figure 11: Example of Min/Max analysis results

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4 Theoretical background

To evaluate composite structures, the user must be familiarized with theory of composite structure

failures. This chapter provides only basic overview of failure criteria used in the COMPOST-

SOFTWARE. Please note that some of implementation details are not mentioned in this chapter for

brevity. We encourage users to have a look inside references and source codes for further details.

4.1 Failure indices

The COMPOST software uses failure indices to express the failure of given structure. Failure indice

is defined as

stressallowed maximum

stresscurrent=FI

Therefore failure indices greater than one, indicates that the structure is likely to fail.

4.2 General notation

Figure 12 presents a notation, which is usually used in classic laminate theory. There are two

coordinate systems:

Xm,Ym,Z - Element coordinate system

1,2,Z - Layer coordinate system, axis 1 is parallel to fiber direction

Ribbon - Direction of honeycomb expansion.

Figure 12: Sandwich structure coordinate system

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4.3 Laminate failures

To evaluate laminate failures, the COMPOST-SOFTWARE uses exactly same equations as

provided by FAA/AR-95/109. Not all failure criteria from this circular are implemented in the

COMPOST-SOFTWARE yet.

Laminate failure criteria are based on classic laminate theory and are calculated for each layer

separately. There are two kinds of laminate failure criteria:

Non-interactive criteria: Failure indices depend on one stress value and one allowable value.

Interactive criteria: Failure indices depend on multiple stress values.

4.3.1 Max stress

Maximum stress is non-interactive failure criterion. It provides three failure indices in fiber

direction, perpendicular to the fiber direction, and shear failure.

X

σ=FI 1

1

Y

σ=FI 2

2

S

τ=FI 12

12

Where:

σ1 - Stress in fiber direction

σ2 - Stress in direction perpendicular to the fiber direction

τ12 - Shear stress

X - Maximum allowable stress in fiber direction

Y - Maximum allowable stress in direction perpendicular to the fiber direction

S - Maximum shear allowable stress

Maximum allowable stresses X,Y are dependent on stresses σ1,σ2. Where stress is compressive, a

compressive strength must be used. Where stress is tensile, a tensile strength must be used.

4.3.2 Tsai Wu

Tsai-Wu is interactive failure criterion. The interaction is done by following equation:

21

2

12

2

2

2

121 2 σσF12+τF66+σF22+σF11+σF2+σF1=FI

Where:

18

TC X+

X=F1

11

F2 =1

Y C

+1

Y T

TC XX=F11

1

TC YY=F22

1

2

1

S=F66

TC XX=F12

2

1

Where:



XC - Compressive strength in fiber direction

XT - Tensile strength in fiber direction

YC - Compressive strength in direction perpendicular to the fiber direction

YT - Tensile strength in direction perpendicular to the fiber direction

S - Shear strength

4.3.3 Tsai Hill

Tsai-Hill is another interactive criterion. The interaction is done by equation:

2

12

2

2

2

2

21

2

2

1

S

τ+

Y

σ+

X

σσ

X

σ

Where:



τ12 - Shear stress

X - Maximum allowable stress in fiber direction

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Y - Maximum allowable stress in direction perpendicular to the fiber direction

S - Maximum shear allowable stress

Maximum allowable stresses X,Y are dependent on stresses σ1,σ2. Where stress is compressive, a

compressive strength must be used. Where stress is tensile, a tensile strength must be used.

4.3.4 Hashin

Hashin is interactive criterion, which produces three failure indices: fiber compressive failure, fiber

tensile failure and matrix failure.

C

CX

σ=F 1

2

12

2

1

S

τ+

X

σ=F

T

T

2

12

2

2

S

τ+

Y

σ=F

T

M

Where:



XC - Compressive strength in fiber direction

XT - Tensile strength in fiber direction

YC - Compressive strength in direction perpendicular to the fiber direction

YT - Tensile strength in direction perpendicular to the fiber direction

S - Shear strength

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4.4 Failures of a sandwich with an isotropic core

4.4.1 Wrinkling

Wrinkling is considered as local short wave-length buckling of sandwich face sheet, which is

subjected to a compressive stress. Structures, in which the wrinkling occurs, lose their stability very

quickly, usually with fatal consequences. This is due very low post-wrinkling load carrying

capability of such structures. Usual way to fix problems related to the wrinkling is improving face

sheets stability and improving bond adhesion between face-sheets and core.

To evaluate the wrinkling failure in sandwich with isotropic core, the load is transformed to load in

material directions of core layer. Therefore a recommended orientation of the core is 0 deg. Two

limit stresses in core directions are established by following equations:

Limit stress in main principal direction:

3

1

GcEcEfk= x1xw

Limit stress in minor principal direction:

3

1

GcEcEfk1= yyw

Where:

k1 - User constant, usually suggested 0.63

Ef - Flexural elastic modulus of given face-sheet in principal directions

Gc - Core shear modulus

These two limit stresses are combined together:

yx

ywyxwx

wr+

+=

Figure 13: Sandwich wrinkling failure example

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If the minor principal stress is compressive, the failure indice is determined by following equation:

23

1

wr

xy

wr

3

y

3

x+

K

+=FI

If the minor principal stress is tensile, the failure indice is determined by following equation:

2

wr

xy

wr

x +K

=FI

Where:

σx - Stress in major principal direction

σy - Stress in minor principal direction

K - Constant K=1

4.4.2 Flexural core crushing

Flexural core crushing usually occurs during bending, when the bending moment is high and the

core compressive strength is insufficient. The COMPOST software uses following equation to

determine the core crushing failure:

Call

zy

2

y

zx

2

x

σ

Dd

M+

Dd

M

=FI

Where:

Mx, My - Applied bending moments per unit length

d - Distance between faces (flanges)

Dz,x , Dz,y - Bending stiffness from ABD matrix

σCall - Core compressive strength

Figure 14: Core crushing failure example

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4.4.3 Shear crimpling

Shear crimping is general instability failure of given element, which is a short wavelength form of

antisymmetric wrinkling. Usually is caused by a low shear modulus of the core. The COMPOST

software uses following equation to determine the crimpling failure:

ctG

N=FI

1z

Where:

N - Force per unit length

G1z - Core shear modulus

tc - core thickness

4.4.4 Core shear failure

Transverse shear failure occurs when the core shear allowable strength is exceeded. When the

design employs webs wrapped around the core and flanges, this failure is unlikely to occur, since

webs will carry more shear load, than the core. The COMPOST software uses following equation to

determine the transverse shear failure:

fSall

2

32

kσ

τ+τ=FI

2

31

Where:

τ1,3, τ2.3 - Transverse shear stresses

σSall - Core shear strength

kf - User constant

Figure 15: Shear crimping failure example

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4.5 Failures of a sandwich with a honeycomb core

4.5.1 Wrinkling

In case of wrinkling failure, one must differentiate between types of sandwiches. Wrinkling failure

on sandwiches with isotropic cores is described above.

The approach at sandwiches with honeycomb cores is basically the same as in sandwiches with

isotropic cores. Load is transformed into ribbon direction of element (figure 12). Two limit stresses

in core ribbon direction are established by following equations:

Limit stress in ribbon direction:

cfx

fc

fxxwtE

tEEk2=

Limit stress in direction perpendicular to ribbon direction:

cfy

f

fyxwtE

tEcEk2=

Where:

k2 - User constant, usually suggested 0.82

Ef - Flexural elastic modulus of given face-sheet in principal directions

Ec - Elastic modulus of the core

tf - Thickness of given face-sheet

tc - Thickness of the core

Otherwise, the work flow is exactly the same as in case of sandwiches with isotropic cores.

4.5.2 Dimpling

Intracell dimpling is a local instability of sandwich face-sheets, where the face-sheet buckles

between cell walls.

Figure 16: Sandwich dimpling failure example

24

Two limit stresses in ribbon directions are established by following equations:

Limit stress in ribbon direction:

2

21121

2

s

ffx

xdc

t

μμ

E=

Limit stress in direction perpendicular to the ribbon direction:

2

21121

2

S

ffy

ydc

t

μμ

E=

Where:

Ef - Flexural modulus in ribbon direction / perpendicular to the ribbon direction.

tf - Thickness of given face-sheet

cs - cell size

Stresses are combined together:

yx

ydyxdx

dp+

+=

Where:

σx - Stress in ribbon direction

σy - Stress in direction perpendicular to the ribbon direction

Failure indice is given by:

2

8.0

n

1

dp

xy

dp

n

y

n

x+

K

+=FI

Where “n” depends on ratio cell size and thickness of face-sheet:

If 15.63F

S

t

C then n=3

If 15.63<t

C

F

S then

2

15.632

F

S

t

C+=n

25

5 Acknowledgments

6 APPENDIX

6.1 Reporting bugs

Please send your bugs description on [email protected] We would like to improve the

COMPOST-SOFTWARE and fix bugs, you will find in it. Please remember, we are not employed in

COMPOST-SOFTWARE, therefore doing that may take us little bit longer.

7 References:

[1] ASM International Handbook Committee, ASM Handbook, Volume 21, December 2001,

ISBN: 0-87170-703-9

[2] Bruhn, E.F., “Analysis & Design of Flight Vehicle Structures”, January 1965, C12.5.3.

[3] Ley R.P., Lin W. Mbanefo U. Facesheet Wrinkling in Sandwich Structure, NASA/CR-1999-

208994

[4] MSC. Nastran 2012, Quick Reference Manual, Santa Ana CA, November 2011

mailto:[email protected]

Documents

COMposite POST - Letecký ústavmalis/compost/compostEN_2.pdf · ABAQUS, NX Nastran can be ... restrictions for composite modeling, ... Recommended way to define the PCOMPG is a laminate