Computational methods for simulating and predicting progressive fracture in fiber composite structures are presented. These methods are integrated into a computer code of modular form. The modules include composite mechanics, finite element analysis, and fracture criteria. The code is used to computationally simulate progressive fracture in composite laminates with and without defects. The simulation tracks the fracture progression in terms of modes initiating fracture, damage growth, and imminent global (catastrophic) laminate fracture

Chamis, C. C.

English

NASA Technical Reports Server

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NASA Technical Memorandum
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Computational Simulation of Progressive _ i
Fracture in Fiber Composites __ , _i
{SaSA-TS-87341) COZPUTaTIGNAt SZSULaTIOS OF
P_OG_.SSIVE F_AC_t_E IN FIBER CC_POBI_ES
{NASA) 12 p _C A02/_ A01 CSCL 11D
G3/2_
Christos C. Charnis
Lewis Research Center
Cleveland, Ohio
4
Prepared for the
International Conference on Computational Mechanics
spomored by the International Committee on Computational Mechanics
Tokyo, Japan, May 25-28, 1986
1186-2E3.76 ..........
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COMPUTATIONAL SIMULATION OF PROGRESSIVE FRACTURE IN FIBER COMPOSITES
Chrlstos C. Chamls
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
SUMMARY
Computational methods for simulating and predicting progressive fracture
in fiber composite structures are presented. These methods are integrated into
a computer code of modular form. The modules include composite mechanics,
finite element analysis, and fracture criteria. The code is used to computa-
tlonally simulate progressive fracture in composite laminates with and without
defects. The simulation tracks the fracture progression in terms of modes
initiating fracture, damage growth, and imminent global (catastrophic) laminate
fracture.
INTRODUCTION
Prediction of progressive fracture of composite laminates is fundamental
to developing the methodology for quantifying composite structural durability
and reliability. NASA Lewis Research Center is conducting fundamental theo-
retical and experimental research programs to develop formal methods and pro-
cedures for determining progressive composite fracture. The theoretical
studies include the development of composite mechanics, combined stress fail-
ure criteria, criteria for identifying predominant fracture modes and asso-
ciated fracture surfaces, and the development of integrated computer codes for
the computational simulation of progressive fracture In fiber composites.: The
experimental studies include development of methods for real time ultrasonic
C-scan of laminates under _ad in order to detect fracture initiation, damage
growth and fracture progression as these events occur. The experimental
studies also include development of methods for post-mortem examination of
fracture surfaces in order to identify and catalog unique fracture surface
characteristics associated wlth dominant fracture modes.
The theoretical studies previously mentioned led to the development of
computational methods for assessing composite structural behavior (lhtegrlty,
durab111ty and damage tolerance). A major portion of the computational method¢
development includes the computational simulation of progressive fracture in
composites which is the subject of this paper. This simulation Is described
in terms of (I) the various composite scales (as defined later) and types of
fracture modes that occur in these scales, (2) an integrated computer code to
perform the simulation, and (3) application of the code to predict progressive
laminate fracture.
FUNDAMENTAL CONSIDERATIONS
Progressive fracture in fiber composites is a dynamic (real-time) physical
process. This process is an accumulation of multiple events triggered by the
various stress states and their attendant failure modes present in fiber com-
posites. The various failure modes take place at different scales (levels) In
the composite. The different levels include: (I) sub-micro scale (Intra or
within each constituent and the interphase), (2) micro scale (inter-con-
stituent), (3) macro scale (individual plies and Interplles), (4) laminate
scale (all plies in a llne through the thickness of the laminate), (5) local
scale, a small region defined by neighboring points in the laminate plane (for
example, nodes connecting a finite element) and, (6) global scale (the struc-
tural component).
Because of the several failure modes in each scale, fracture can occur as
single events at different times in different locations in the composite
structure. Or It can occur simultaneously as multiple events in one or more
locations in the composite structures. In view of this, it is convenient to
discuss progressive fracture using the following definitions: (1) failure
initiation - when the stress field induces a failure in the sub-mlcro scale,
(2) defect or f_aw formation - when one or more sub-mlcro scale failures
coalesce to form a micro scale failure, (3) ply failure - when several micro
defects coalesce to form defects in the macro scale (transply cracks),
(4) delamlnatlon - when a defect is formed between adjacent plies, (5) laminate
failure - when macro defects (transply cracks) coalesce to form a through-the-
thickness laminate defect or crack, (6) progressive fracture - when laminate
defects progress In the plane of the laminate to form defects in the local
scale, and (7) global fracture - when the composite structure fractures in one
or more parts. Events occurring in items (I) to (6) are usually combined and
are collectively called laminate or composite damage.
Computational simulation of progressive fracture in composites as a real-
time dynamic event has not yet been investigated to the author's knowledge.
Also, computational simulation of progressive fracture as an equivalent static
process starting from the sub-mlcro scale has not yet been investigated. The
computational simulation presently pursued at Lewis is based on the macro scale
and it assumes that progressive fracture _s an equivalent static process. In
this computational simulation, macro scale defects (transply cracks) are formed
when the stress field induces failure in one of the ply failure modes (longi-
tudinal tension or compression, transvers_ tension or compression and Intra-
laminar shear) and/or induces Interply delamlnation. The corresponding ply and
Interply strengths are predicted using composite mlcromechanics. The composite
mlcromechanics account for void and hygrothermal effects on the constituents
and, therefore, on the ply and Interply strengths. Composite micromechanlcs
integrate, in part, the events occurring at the sub-micro and micro scales.
COMPUTATIONAL SIMULATION USING CODSTRAN
Research activities on progressive composite fracture at Lewis during the
last ten years have culminated in the development of the CODSTRAN computer code
(ref. I). CODSTRAN (Composite Durability Structural Analysis) has been speci-
fically developed for the computational simulation of p_ogresslve fracture in
fiber composites.
CODSTRAN is a modular program (fig. I) that does quantitative calculations
to predict defect growth and progressive fracture in composite structural com-
ponents. Capabilities of CODSTRAN include determining the durability of com-
posltes with and without defects, determining structural responses due to
mechanical and thermal loads, accurate prediction of stress states near
defects (stress concentrations), and prediction of ply and laminate level
failure and fracture. The modules comprising CODSTRAN are: (I) the executive
module, containing communication links to all other modules; (2) the I/O
module; (3) the Analysis module; (4) the Composite Mechanics Module; and
(5) the Fracture Mechanics module.
The Analysis module Is NASTRAN (ref. 2) and Is used to calculate both
near-fleld and far-fleld stresses In a finite element model of the structural
component or specimen. The Composite MeChanics module (MFCA) (ref. 3) gen-
erates laminate properties from constituent properties (composite mlcrome-
chanlcs) and uses Intraply failure and Interlamlnar delamlnatlon criteria to
check ply and Interply failure, respectively. The Fracture Mechanics module
Is able to account for both ply level fracture and laminate fracture. The
modified distortion energy principle and/or a general quadratic surface flt are
used to indicate combined ply level fracture (ref. 4). Laminate level failure
Is based on concepts described In references 5 and 6. It Is assumed to occur
when all the plies In the laminate have failed.
To computatlonally simulate progressive fracture, COOSTRAN uses an Iter-
atlve procedure whereby a load Is applied to the finite element mesh of the
structure belng modeled. The response of the structure to the load can be no
damage, damage, or destruction of an element(s) (local fracture). Based upon
thls response, the load increment Is updated as follows: (1) If no damage Is
predicted, the load Is updated by some predetermined load increment; (2) If
elements are damaged or destroyed (defect growth or local fracture), the same
load is re-applled with reduced material properties assigned to the damaged
elements. Destroyed elements are purged from the finite element mesh, effec-
tively defining progressive fracture. Thls load Is maintained until equilibrium
in the structure is achieved. Equilibrium is defined as the point where'the
structure, with Its updated geometry and modified material properties, can
sustain the applied load without the occurrence of further damage. This Iter-
atlve procedure Is continued through load increments until global fracture of
the structure occurs. This Iteratlve procedure Is depicted schematlcally in
figure 2.
1
PROBRESSIVE FRACTURE - TYPICAL RESULTS
CODSTRAN has been used to computatlonally simulate progressive fracture
In a composite laminate with a center notch depicted schematically In figure 3
(ref. I). These laminates were made from Thornel 300 graphite fiber In an
epoxy matrix (T3OO/E). The laminate configuration Is [0/+30/0/-30/012s wlth
about O.OOfi In. ply thickness. These types of laminates were loaded to frac-
ture in axial tension. The finite element model used In the simulation Is
shown In figure 4.
Progressive damage and fracture results obtained are suntmarlzed In figure
5 at several load levels indicated as a percentage of the fracture load. First
damage indication appeared at 33 percent of the load. The damage continued to
grow and extend until the load was increased to 100 percent of the fracture
load. _t thls load CODSTRAN looped through several iterations. The first
Iteration, caused the extended damage shown In the first lO0 percent schematic
.Infigure 5. The last iteration destroyed all elements to the right of the
cracks, indicating laminate global fracture utth some bending as shown tn the
last schematic In figure S.
CODSTRANhas also been used to study the damage growth and progressive
fracture of laminates without defects, wlth center slits and wlth center holes
(refs. 7 and 8). Progressive fracture results from thls study are summarized
In figure 6 at zero load and at fracture load, first iteration. As can be seen
the progressive fracture Is about the same for the laminates wlth the sllt and
wlth the hole. It is Interestlng to not_ that progressive fracture initiated
at the center of the laminate without defects and advanced in generally similar
directions as that In the laminates with the defects.
COOSTRAN keeps records of all the modes that initiate fracture at the
macroscale (ply and Interply) levels. A typical output of these records is
summarized In Table I for the laminates shown in figure 6 and for different
laminate configurations [±es]. These results provide considerable details
wlth respect to weak modes In the laminate and with respect to Its structural
integrity and/or damage tolerance. In addition to records of fracture modes,
CODSTRAN keeps records of plies destroyed, elements destroyed and nodes which
do not connect elements. All thls information Is necessary to track the damage
(defect growth and progressive fracture) at the various scales within which It
occurs.
In order to assess the fracture toughness and service llfe of the laminate,
CODSTRAN continued to track the crack or defect opening In either the local
scale (between two adjacent nodes) or global (overall displacements) scale.
Typical results for local crack opening displacement In laminates wlth center
slits are shown in flgure I for two laminate configurations. The results for
the [_+45]s laminate show unbounded crack opening displacement for the same
load and, therefore, imminent global (catastrophic) fracture once progressive
fracture began. The results for the [0]4 laminate showed several IncreasSs
In load were required prior to imminent global (catastrophic) failure.
CONCLUSIONS
Progressive fracture in fiber composites can be computatlonally simulated
using an integrated computer code such as CODSTRAN. The computational simu-
lation tracks failure initiation, defect growth and damage, at the various
scales In which these events occur. The computational simulation of pro-
gressive fracture provides extensive detailed information which can be used to
detect failure initiation modes, damage growth (magnitude and direction), pro-
gressive fracture direction, and imminent global fracture. All thls infor-
mation makes it possible to computatlonally assess the structural integrity,
damage tolerance and service llfe of fiber composite structures.
REFERENCES
I. Chamls, C.C.; and Smith, G.T.: CODSTRAN: Composite Durability Structural
Analysis. NASA TM-790_O, 1978.
2. McCormick, C.W., ed.: NASTRAN User:s Manual (level 15). NASA SP-222(01),
1972.
3. Chamls, C.C.: Computer Code for the Analysis of Multilayered Fiber
Composites - User's Manual. NASA TN D-7013, 1973.
T
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B
chamis, c.c.: Failure Criteria for Filamentary Composites.
Composite Materials: Testing and Oeslgn, ASTM-STP-460, ASTM, 1969,
pp. 336-351.
Sinclair, J.H.; and Chamls, C.C.: Fracture Surface Characteristics of
Off-Axis Composites. NASA TM-73700, 1977.
Sinclair, J.H.; and Chamts, C.C.: Mechanical Behavior and Fracture
Characteristics of Off-Axis Fiber Composites. I - Experimental
Investigation. NASA TP-1081, 1977.
Irvtne, T.B.; and Gtnty, C.A.: PrOgressive Fracture of Fiber Composites.
NASA TM-83701, 1983.
Glnty, C.A.; and Irvlne, T.B.: Fracture Surface Characterl_tlcs of
Notched Angleplled Graphlte-Epoxy CompositeS. NASA TM-B37B6, 19B4.
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TABLE I. - FRACTURE MODE a OF [±e] s G/E LAMINATES
(PREDICTED BY CODSTRAN)
Notch type
Unnotched
solid
Notched
thru sllt
Notched LT LT LT S
thru hole S S S
aLT = Longitudinal tension
TT = Transverse tension
Ply configuration: [_+e]s; e in degrees
0 3 5 10 15 30 45 60 75 90
• , |
LT LT LT LT I S I TT TT TT
S3 S3 S3 S S
LT LT LT S S I I I TT TT
S1 S S S S TT
S2
S I I I TT.ITT
LT S S TT
TT
S = Intraply shear: I) Intraply shear occurring
around notch tip during
progressive fracture
2) Minimal Intraply shearing
during fracture
3) Some Intraply shear occurring
near constraints (grips)
I = Interply delamlnatlon
r
IAPPROX. I
SEMI-EMPIRICALI
SPECIALFINITE -J
ELEMENTS
NASTRAN
STATIC r I
CYCLIC FRACTURE
DYNAi'C "-_ CRITERIA I
I LIFEPRED I l I COMPOSITE ]
I MOOULES MECHANCSI
J ANALYSIS L_l EX_UTiVE L_--.I NPUTMODULES I TM [ MODULE J I MODULE
+ L
DEFECTGROWTH RATE"
RESIDUALSTRENGTH
SERVICELIFE
INSPECTIONINTERVAL
REPAIR
FigureI.- CODSTRAN computercodeschematic.
COMPONENT GEOMETRY
DEFECTGEOMETRY
MATERIALPROPERTIES
FRACTURE DATA
FATIGUEDATA
SERVICEDATA
!
I LOAD JINCREMENTED
INPUTMODULE I
CGMPONENT GEOMETRY,DEFECTGEOMETRY,I
COMPOSITETYPE,LAMINATECONFIGURA- I
TION, SERVICEENVIRONMENT I
COMPOSITEMECHANICSMODULE I
IGENERATELAMINATEPROPERT(FSFORFINITELEMENTANALYSIS
+
ANALYSISMODULE I
NASTRANUSEDFORBOTHTHENEAR-AND
FAR-FIELDSTRESS AND DISPLACEMENT
SOLUTIONS
COMPOSITEMECHANICSMODULE I
ICOMPUTE PIY AND INTERPLYSTRESSES
FRACTURE CRITERIAMODULE I
IPLY LEVELFRACTURE,INTERPLYFRACTURE CR TERA
COMPOSITEMECHANICS MODULE I
ICHECK FOR PLY AND INTERPLYFAILUREONAN ELEMENTBY ELEMENTBASIS
LIFEPREDICTIONMODULE
PLYFAILURE,ELEMENTFAILURE,AND
DEFECTGROWTH(CRACKOPENING)
SAME LOAD,
MODIFY
MATERIAL
PROPERTIES
I OUTPUT_OOULE
CRA('XOPENINGDISPLACEMENT,FRACTURE
MODE. NASTRANOUTPUT
NO _ YES _
: _ PLY FAILURE,ELEMENT /
_'''_A;LURL/ I END,F(_OMPLETE
_""- I .LAMINATEFRACTURE
Figure2. - CODSIRAN flowchart: computationalsimulationof progressive fracture.
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Figure5. -Computationallysimulated_rogressive fracture at various
percentagesof the fracture load(15 402Ib; Gr/E[O/+30/OI-30/OI2s).
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OF POOR QUALITY
LOAD:
t-"T"T-l_r t
0 Ib
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LOAD: 5000Ib
F 1--I-1--
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I
: ,I
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2350Ib 2125Ib
Figure 5. - Computationallysimulatedprogressive fracture
of I=minateswith different typesofdefects_Ge/El_Slsl,
•015 _ P
/ FRACTURE l
• 012 _ FRACTURE , _L --
_ • ............. ±
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Figure 7, - Computationaffysimulatedlaminate behaviorto fracture (Gr/Ef_ls),
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1. Report No. 2. Government Accession No. 3. Re_lplent'e Catalog No,
NASA TN-87341
5. Report Date4, Title and Subtitle
Computational Slmu]atton of
In Flber Composites
7. Author(si
12.
Chrlstos C. Chamts
PerforMing O_snlzatlon Name and Address
National Aeronautics and Space
Lewis Research Center
Cleveland, Ohlo 44135
Sponsoring Agency Name end Address
Natlonal Aeronautics and
Nashlngton, 0.C. 20546
Progressive Fracture
=,
15.
Admlnlstratlon
Space Administration
6. Performing Organization Cod,',
505-63-31
8. Performing Organization Report "No.
E-3090
10. Work Unit I_'o.
,= ,, ,,
11. Contract or Grant No,
13. Type of RePort and Period Covered
Technical Hemorandum
14. Sponsoring Ag6ncy Code
Supplementaw Notes
Prepared for the International Conference on Computattona]
by the International Committee on Computational Mechanics,
Ray 25-28, 1986.
Rechantcs sponsored
Tokyo, Japan,
16. Abstract
Computational methods for simulating and predicting progressive fracture tn ftber
composite structures are presented. These methods are Integrated 1nee a computer
code of modular form. The modules tnclude composite mechanlcs, ftntte element
analysis, and fracture criteria. The code ls used to computattonally slmulate
progressive fracture In composite laminates wtth and wlthout defects. The simu-
lation tracks the fracture progression In terms of modes lnlt_atlng fracture,
damage growth and lmrntnent global (catastrophic) lamtnate fracture.
1?. Key Words (Suggest_ by Authoqs))
Computer program; Failure modes;
Composite mechanics; Failure Initiation;
Damage growth; Local fractuPe; 61obal
fracture
19. 8_urity Gist|if. Df this re.re)
Unclassified
18, Distribution Statement'
Unclassified - unlimited
STAR Category 24
_. S_urlty Cles|if, _f this _ge) 21. No. of Hges
Unc]asstfled
22. Pdce*
"For =aia by the National Technical Information Service, Springfield, Virginia 22161


Computational simulation of progressive fracture in fiber composites

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