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8/18/2019 Optimization of Laminate Composite Structures
http://slidepdf.com/reader/full/optimization-of-laminate-composite-structures 1/18
Optimization of Laminate
Composite Structures – RecentAdvances and ApplicationsBy Warren Dias on October 13, 2011
inShare
The use of fiber-reinforced composite material entered a ne era hen
leadin! aircraft O"#s too$ an unprecedented step to desi!n and
manufacture essentially full composite airframes for commercial airliners%
&omposite structures offer unmatched desi!n potential, since the laminate
material properties can be tailored almost continuously throu!hout the
structure% 'oe(er, this increased desi!n freedom also brin!s ith it ne
challen!es for the desi!n process and softare technolo!y%
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)n recent years, *ltair has de(eloped a comprehensi(e frameor$ for
composite optimi+ation% The process consists of three optimi+ation phases%
hase 1 focuses on !eneratin! ply layoutshape concepts throu!h free-si+e
optimi+ation. hase 2 further refines the desi!n by determinin! the number
of plies for a !i(en ply layout defined by hase ), usin! si+e optimi+ation
techni/ues. then hase 3 completes the final desi!n details throu!h ply
stac$in! se/uence optimi+ation, satisfyin! all manufacturin! and
performance constraints% This three-phase process desi!n methodolo!y
has seen increasin! adoption amon! aerospace O"#s, amon! others, as
demonstrated by the Bombardier application process described in this
article%
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Three-Phase Laminate Composite Design Optimization Process
Figure 1 illustrates the different phases of the optimization process.
i!ure 1%
Phase 1: Concept design of material orientation and placement through free-size optimization
The optimization prolem can e stated mathematicall! as follo"s#
$here represents the o%ective function& and represent the j'th constraint response
and its upper ound& respectivel!. M is the total numer of constraints& NE the numer of
elements and Np the numer of super'plies( is the thic)ness of the i'th super'pl! of the k 'th
element. The concept of a *super'pl!+ is introduced to allo" aritrar! thic)ness variation of a
given fier orientation at a given stac)ing location. T!picall! onl! one super'pl! is needed for
each availale fier orientation. ,uring this design phase& responses of a gloal nature are
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considered for oth the o%ective and constraints. T!picall!& compliance or )e! displacement
responses are used to formulate the design prolem so that the overall structural stiffness is
optimized. -anufacturing constraints are important for composite design and need to e address
right at the eginning of the concept design phase. A couple of commonl! used manufacturing
constraints are the percentage of a given fier orientation in the overall thic)ness and the total
laminate thic)ness.
Phase 2: Design fine-tuning using ply-bundle sizing optimization
The free'size optimization descried in hase 1 leads to a continuous distriution of thic)ness for
each fier orientation. A discrete interpretation of the thic)ness defines the la!out of pl!'undles
"ith each undle representing multiple plies of same orientation and la!out/shape. The pl!'
undle la!out can e simpl! otained ! capturing different level'sets of the thic)ness field of
each fier orientation. The default method provides a good alance et"een the true
representation of the thic)ness field and the comple0it! of the pl! tailoring. These pl!'undles of
different fier orientations are then stac)ed together so as to e uniforml! distriuted in the
gloal stac).
n this phase& the design variales are optionall! discrete thic)nesses at unit pl! thic)ness
increments. Also at this design stage& all detailed ehavior constraints& including pl! failure&
should e considered. -anufacturing constraints& such as orientation percentage considered in
hase 1& are carried over during this design phase.
Phase 3: Detailed design through ply stacking sequence optimization
Though the design achieved in hase 2 contained all pl! shapes and stac)ing details& it is li)el!
that detailed manufacturing constraints or pl! oo) rules are not satisfied. Therefore& the stac)ing
se3uence of individual plies is optimized during this phase to satisf! manufacturing constraints
"hile preserving all ehavioral constraints. mportant manufacturing constraints include# 4a5
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limit on consecutive plies of the same orientation( 45 pairing of 6/' angles( 4c5 pre'defined cover
la!'ups( 4d5 pre'defined core la!'ups.
Draping modeling
$hen shell surfaces have i'directional curvature& fier orientation flo" is rather comple0 and
needs to e determined ! draping anal!sis. Often cuts& called darts& need to e placed to
eliminate e0cess cloth "hen a pl! is placed over a curved surface. An e0ample of draping is
sho"n in Figure 2. n such cases& a correction of fier orientation and thinning needs to e
considered in the F7A model. The ,RA7 card is implemented in OptiStruct to accommodate
this correction information otained ! draping anal!sis soft"are.
Zone-based free-sizing
This design/manufacturing re3uirement "as driven ! some commercial aircraft O7-. Their
design process re3uired constant pl! thic)ness for each zone& defined ! intersected stringers and
ris. 8esides simplif!ing pl! la!out& the main reason for the re3uirement is to accommodate
legac! design criteria "here each aforementioned zone is a panel unit for strength and stailit!
evaluation. Therefore constant thic)ness "ithin each panel is re3uired for accurate calculation of
its properties. An illustrative e0ample is sho"n in Figure 9 "here free'size results "ith and
"ithout zone'ased pattern grouping are compared.
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i!ure 2 ly orientation drapin! on a half sphere%
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i!ure 3 Thic$ness distribution of ree-Si+e results ith and ithout pattern
!roupin!%
Application example
The three'phase composite design process is demonstrated through the design of the "ing of a
"ide' od! aircraft& sho"n in Figure :. ;ine load cases of )e! significance are considered. n
this simplified e0ercise& onl! "ing tip displacement constraints are considered& "ith upper
ounds not e0ceeding those of a aseline aluminum "ing under each load case. Onl! the caron
fier composite top and ottom s)ins are optimized. l! orientations availale are <& 6:=/':=& ><
plies& "ith the leading edge as reference.
Phase 1: Concept design !ree-size optimization
-anufacturing constraints considered include#
#aimum thic$ness of each fiber orientation 10 mm
456-56 plies to be balanced
7 mm total laminate thic$ness 32 mm#inimum percenta!e of a(ailable fiber orientations 8 109
The thic)ness distriution of the four fier orientations is sho"n for the upper s)in in Figure =. t
can e seen that pl! alancing constraints )ept the thic)ness distriution of 6:= and ':=
orientations identical.
i!ure 5 &omposite in! model of a ide body aircraft under cruise loadin!%
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i!ure 6 Thic$ness distribution of the upper s$in of the in!%
Phase 2: Design fine-tuning Ply bundle sizing optimization
The results sho"n in Figure = are interpreted into four pl! la!outs for each fier orientation. The
pl! coverage area decreases as the thic)ness level'set increases. The first pl! undle covers the
entire "ing. La!outs of the second pl! undle of < degree orientations for oth lo"er and upper
s)ins are sho"n in Figure ?. ;ote that t!picall! some manual editing of the ra" level'set ased
pl! shape is needed. For simplicit!& this e0ample simpl! adopted the automaticall! generated pl!
shapes defined ! the thic)ness level'sets.
i!ure : Second ply-bundle layouts of the 0 de!ree orientation%
n this stud!& the sizing optimization prolem remained the same as in hase 1. For more realistic
applications& this optimization phase should consider all detailed design criteria& such as strength
and stailit! constraints. The numer of plies in groups of </6':=/>< pl!'undles is# /1='9'1/1'
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1<'=/1='1='>/1='1='19/& @B1 "hich can e determined after the sizing optimization. The total
thic)ness contour of upper s)in after sizing optimization is sho"n in Figure D.
i!ure ; Total thic$ness contour of upper s$in after si+e optimi+ation%
Phase """: Detailed design Ply stacking sequence optimization
This optimization phase focuses on the laminate stac)ing se3uence "hile preserving oth
manufacturing and performance constraints. Additionall!& it is re3uired that certain pl! oo)
rules e applied to guide the stac)ing of plies ased on specific re3uirements. Some pl! oo)
rules that control the stac)ing se3uence are#
– -a0imum numer of successive plies of a particular fier orientation
– airing of the 6 and – :=s
– dentif!ing a se3uence for the core and cover regions
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For this e0ample& the optimization prolem as previousl! formulated in the sizing phase is
retained& and the follo"ing additional pl! oo) rules are applied# 4a5 the ma0imum successive
numer of plies does not e0ceed three plies( 45 the 6 and – :=s e reversed paired. Figure E
illustrates the stac)ing se3uence efore and after stac)ing optimization. Through this proof'of'
concept stud!& the three'phase optimization process has successfull! demonstrated its capacit!
for ma0imizing utilization of the potential of composite material in the design of a laminate
composite structure& "hile significantl! shortening the design process.
i!ure 7 Stac$in! optimi+ation < initial and final stac$in! se/uence%
Application of Altair’s composite design optimization process to aero-structure composite
component development at Bombardier
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This section outlines application of the Altair composite optimization technolog! to composite'
component design at 8omardier. As part of 8omardiers ongoing technolog! development
initiatives& application of the process "as e0plored at single and multiple component levels. A
description of the process and method of application inside a d!namic aerospace design
environment is descried. -ethods for incorporating structural and manufacturing constraints
are introduced. Also summarized are the interfaces developed et"een design and stress groups&
"hich underpin the successful application of the technolog! in an environment "here design
re3uirements can fre3uentl! change.
"ntegration of #ltair$s composite design process
ntegration of Altairs composite optimization process "ith the design process and all of the
necessar! interfaces is sho"n schematicall! in Figure >. The main additions to the process are
interfaces accommodating inputs and outputs to and from the design team. ;otal!& custom
responses and constraints are needed to align the optimization "ith strength& stiffness and
stailit! 3ualification re3uirements. 70port of the optimization solution is also re3uired in a
numer of different formats& including CA,'format laminate descriptions& 3ualification reportsummaries and additional finite' element formats.
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i!ure = Schematic Summary of the )nte!ration of *ltair>s &omposite Desi!n
Optimi+ation rocess ith Bombardier>s *ero-Structure Desi!n rocess%
Composite optimization interfaces
A revie" of the 8omardier aero'structure design process "as performed to identif! the inputs
and outputs re3uired for the composite optimization process. Successful access to the
technolog! in the overall design process is underpinned ! these interfaces "or)ing efficientl!
and roustl!. The main focus areas for the interface development "ere#
i5 Conversion of 8omardier F7- data to OptiStruct format suitale for
optimization
ii5 F7- e0port at the end of the process
iii5 CA, format e0port of final designs
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iv5 Gualification anal!sis reporting in 8omardier format 4spreadsheets and other
digital documents5
Altairs generic F7- and composite interfaces "ere modified to facilitate each of these
re3uirements in the 8omardier design environment. The resulting solution "as a single
integrated platform that facilitated passage of input and output data to and from the optimization
et"een 8omardier and Altair. Composite specific results visualization and report data could
easil! e shared and revie"ed ! all parties.
%ptimization problem formulation
The optimization prolems "ere t!picall! defined to minimize mass su%ect to stiffness&
allo"ale composite stresses and stailit! criteria. -ultiple load cases "ere defined
and& "here availale& appropriate stiffness targets set for each& ased on the aseline
response.
n addition to the composite laminate sizing design variales for components& shape
optimization of the stiffening memers also "as investigated through FR77 SHA7
optimization in OptiStruct. Ireater design freedom is afforded "ith this approach&
since it allo"s each stiffener height to change independentl! and freel! in shape as "ell
as size. This is often advantageous "here a alance et"een relative stiffness and
stailit! must e maintained. To constrain the optimization to derive designs compatile
"ith the design team re3uirements for some components& zone oundaries "ere defined
over the surface. OptiStruct can constrain the laminate solutions to respect these
oundaries from the first free'sizing stage. This is often a )e! manufacturailit!
re3uirement and can e loc)ed do"n at the concept stage.
Commonalit! et"een manufacturing constraints "as maintained throughout the stages
to enforce minimum percentages of cloths and uni'directional plies in the stac). n the
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later stages& manufacturing rules "ere enforced limiting the ma0imum numer of
consecutive plies.
The structural constraints "ere implemented ! direct sampling of finite'element
results 4stiffness and strain5 or ! custom calculations developed to correlate "ith
3ualification assessment methods 4gloal and local stailit!& additional strength
re3uirements5. The custom calculations "ere implemented through OptiStructs
,R7S9 functionalit!& "hich ensures efficienc! in the handling of custom calculation
routines and response sensitivities.
Discussion
The composite optimization process "as applied successfull! in a real'"orld aerospace design
environment& allo"ing efficient e0ploration of designs and delivering "eight'saving potential for
a range of components and s!stems.
The follo"ing ma%or advantages "ere found from application of the process#
i5 The free'form stage provided an efficient testing ground for design sensitivit!
to applied loads and design constraints. The solutions "ere not influenced !
previous designs and provided insight into methods for improving structural
efficienc!. The! provide a ver! efficient method for performing trade'off
studies and rapid assessment of changes in design re3uirements.
ii5 The process demonstrated the value of loc)ing pl! continuit! into the
optimization from earl! in the process. n this "a!& manufacturailit! could e
constrained "ith less impact on the structural efficienc!. nterfaces "ere
developed et"een the OptiStruct pl!'ased output and design s!stem carr!ing
over pl! continuit! directl!.
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iii5 Significant mass savings "ere predicted from application of the technolog!
and a measure of the effect on "eight of var!ing manufacturing constraints
could e 3uantified.
iv5 The input data and optimization solutions could e integrated "ith the current
design practice at 8omardier& facilitating efficient communication and final
design 3ualification.
Application of the optimization approach at 8omardier has led to a repeatale process& "hich
accommodates the composite design 3ualification re3uirements and can e enhanced and applied
at component and s!stem level.
The three'phase design process starts "ith creating design concepts capale of full! utilizing the
increased design potential of composite material. t finishes "ith a final design of pl!'oo)'level
details "here manufacturing rules& together "ith all performance re3uirements& are satisfied. An
aircraft "ing case stud! is sho"n to demonstrate the optimization process. Then& a detailed
description of the application "ithin a real'"orld aircraft design environment at 8omardier
Aerospace is given. t is particularl! notale that customer'specific design constraints on panel
strength and stailit! are incorporated through e0ternal responses 4,R7S95. These factors
demonstrate the versatilit! of OptiStruct that allo"s the optimization process to fit into an
estalished comple0 environment of commercial'aircraft design.
This paper is written in collaboration with Ming Zhou, Vice President of Software Deelop!ent"
? @earn more about optimi+ation solutions from 'yperWor$s
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• *bout
• @atest osts
Warren Dias
Business De(elopment #ana!er - OptiStruct at *ltair
Warren is the Business De(elopment #ana!er for OptiStruct here his
responsibilities include increasin! the !lobal footprint and usa!e of
OptiStruct% 'e Aoined *ltair in 2000, and no has nearly 16 years of
eperience in the field of finite element analysis and structural optimi+ation%
'e holds a Bachelor De!ree in #echanical "n!ineerin! from #anipal
)nstitute of Technolo!y in )ndia%
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