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Challenges to Current Design Rules Bi-angle Non Crimp Fabric (NCF)
Stephen W. Tsai steve.tsai@mac.com
Stanford University February 28, 2012
This document contains Patent Pending technology of Stanford University and Chomarat
Global team members Location Points of contact Stanford University Stanford, CA Steve Tsai, Melih Papila, Kim Parnell
Chomarat Le Cheylard, France Michel Cognet, Philippe Sanial, T. Roure
Chomarat North America Anderson, SC Brian Laufenberg, John Carson
NASA Space Flight Center Huntsville, AL Alan Nettles
Aldila Composite Materials Poway, CA Fred Saremi
VX Aerospace Morganton, NC Bob Skillen, Ray Jones
University of Bordeaux Bordeaux, France Thierry Lorriot, Nicolas Perry
Kanazawa Institute of Technology Kanazawa, Japan Yasushi Miyano, Masayuki Nakada
Think Composites Antony, France Thierry Massard, Jean P Charles, R. Harry
University of Rio Grande do Norte Natal, Brazil Daniel Melo
Hanyang University Seoul, Korea Sung Ha
University of Porto Porto, Portugal Pedro Camanho
Univ of Dayton Research Institute Dayton, OH Sangwook Sihn
National Univ of Singapore Singapore Tong Earn Tay, Ridha Muhammad
University of Girona Girona, Spain Albert Turon, Josep Costa
15 organizations 8 countries 27 professionals
Composites Workshop – Global Team
Black Aluminum vs Bi-Angle NCF Black Aluminum
• Symmetric • Balanced • [0p/±45q/90r/. . . ]S
• Integer stacking • Micro crack: tolerated • Heterogenous • Ply drop: a black art • 4-axis layup • Primary plane: σ1 vs σ2
• Fixed strain allowable
Bi-Angle NCF • Asymmetric: simple stack • Unbalanced: anisotropic • [0/φ]16T: easy to match plies • Angle φ: continuous variable • Micro crack: suppressed • Homogenized: toughened • Shape-optimized taper • 1-axis layup: 7x faster • Primary plane: σ1 vs σ6
• Strength ratio: scalable
Examples of Traditional Laminates 45 45 45 -45 -45 0 45 0 -45 -45 45 0 0 -45 45
45 0 0 -45 45 -45 45 -45 90 -45 90 45 90 45 0 45 -45 -45 -45 0 0 45 45 45 -45 -45 0 0 0 -45
45 45 16 plies 90 -45 -45 ------Symmetry plane 45 18 plies 90 -45 ------Symmetry plane
20 plies 90 -----Symmetry plane
A B C Traditional laminate design is limited to 4 ply angles and some repeated patterns, mid-plane symmetry, and required [0] and [90] plies to satisfy the 10 percent rule. This procedure is difficult to follow and costly to manufacture. It is nearly impossible to tell if the laminate is optimum, and how to drop plies for tapering laminates. Instead of 8- to 10-ply sub-laminates, we recommend 2 or 3.
(10/80/10)
(22/67/11) (38/50/12)
Percentage of (0/±45/90): Soft Hard
[0/±
454/
90] 2
S
[02/
±45 3
/90]
2S
[03/
±45 2
/90]
2S
Least Number of Plies in Sub-laminates
5 Number of Plies in Sub-Laminates
Num
ber o
f Plie
s Req
uire
d
Simpler and easier laminates
Tool: LamRank, pp 4-21/4-25; Appendix B-4
FPF of [0/φ], where φ = 20, 25, 45, 90
[0] [0] [20]
[25]
[45]
Maximum laminate stress σ1 that causes failure in [0] & [φ], MPa (lower stressed ply controls FPF)
More equally stressed plies = higher FPF
[0]
[90] Uniaxial strength
FPF FPF
FPF Uniaxial strength
X/2 [0]
[0/25] [0/90] [0/20] [0/45] FPF
σ6/σ1 σ6/σ1 σ6/σ1 σ6/σ1
Micro cracking suppressed when plies are matched. Much easier to do with 2 plies
Tool: MicMac-Inplane
Shear Coupling: Deflection/Rotation
Unique [0/φ] NCF at Chomarat
Mass producible NCF with unique thin plies and shallow off-axis angles
Best of both worlds: strength equal to uni-tape laminates, handling ease of
fabrics, and cure in or out of autoclave
Existing 45°
New 25°
Ply Properties of Thin-ply T700NCF • Ex = 140 GPa, Ey = 9.3 GPa, νx = 0.3; Es = 5.8 GPa
• X = 2944 MPa, X’ = 1983 MPa, Y = 66 MPa; Y’ = 220 MPa; S = 93 MPa
• Vf = 64%; 75 GSM; Ef = 210 GPa; Xf = 4900 MPa
1.27 m (50”)
From VX Aerospace
Bi-angle NCF, 150 GSM or 0.125 mm thick
Acoustic Response of [±45/0/90]S Coupons
Event
Energy
Amplitude
Event
Energy
Amplitude
Normal ply thickness: 0.12 mm Thin ply: 0.04 mm
Top and side views of failed coupon, same total thickness Note extensive delamination of thick ply coupon on the left
Note extensive signals after FPF Less signals after much higher FPF FPF at 250 units FPF at 480 units
Thic
k pl
y
Thin
ply
Delamination No delamination
σmax = 70 ksi (70% static), R = 0.1, f = 5 Hz, after 73,000 cycles Ply thickness = 0.04 mm, Laminate thickness = 3.2 mm
THIN THICK Thin ply Thick ply
[45/02/-45/90/45/02/45/0]5S
[455/010/-455/905/455/010/455/05]S
Some splitting and edge delamination Extensive micro
cracking, splitting & edge delamination
Tension Fatigue at RT - (50/40/10)
Symmetric vs Asymmetric Laminates
12
n = 32 n = 32
[0/±45/90]4S [±]16T [±]8S
n = 32 Asymm Symm Asymm
n = 32 Asymmetric Symm Symmetric
Continuous Stacking
Contin Stacking
Asymmetric layup is faster, less prone to error, higher output, and easier ply drop
4-angle 3-angle 2-angle
[0/±45/90]8T
n = 32 n = 32
Contin Stacking
Increasing homogenization
Homogenization of Stiffness and Strength
Repeat index r
Flex and In-plane stiffness, msi
Repeat index r
[±12.5]2rT X
X’
S 1 3 5 7 9
30
20
10
0
Uniaxial and shear strength, MPa
[02/90]rS
Repeating index is the easiest parameter for homogenization of laminates. It is made simpler if the sub-laminate have only 2 angles and also with thin plies
Conditions for homogenization [D*] = [A*]; [B] = 0
2r =
16
Homogenization: Reduces Warpage [0/±45]2rT [0/±25/0]2rT [0/25]2rT
Newly cured Newly cured Newly cured
Long term Long term Long term
ε6f
ε2f
ε1f
Flex
stra
in, 1
0-3
Flex
stra
in, 1
0-3
Repeat index r Repeat index r Repeat index r
32 plies 2 mm thick
64 plies 4 mm thick
72 plies 4.5 mm thick
Tool: MicMac-GenLam; Sections 4.10 and 6.5, and Figure 9.11
[Bi-angle]16T Asymmetric NCF Test Panel
2’ x 3’ x 80 mil thick panel No warpage
Asymmetric stacking, mid-plane symmetry not needed
Ply-by-Ply vs Homogenized Plate
RFPF R(i)
RFPF E1° = 1/a11*, E2° = 1/a22*, . . . nu61° = a61*/a11*
Homogeneous anisotropic plate: one R
Ply-by-ply R(i) of a laminated anisotropic or orthotropic plate
Back to the basics: many closed-form and FEM solutions easily applied; speed increases by n (number of plies) in model formation and stress recovery
Anisotropic Tsai-Wu criterion: F11, . . . F16; F1, F2, F6
R = strength ratio = safety factor
Tool: MicMac-Inplane; Figures 4.21 and 4.22, Sections 8.8, and 9.1
Tapering of Homogenized Laminates • Homogenization makes ply drop strategy practical and fast • Thinnest section should be [0/φ]16T, [0/±φ/0]8T • Ply drop should be by unit bi-angle layer, in 0.125 mm steps • Distance between drops to be 1 mm (8 times drop step) • Taper can be linear, nonlinear, and in 1- and 2-dimensions • Take advantage of shape optimization theories and tools
Min
imum
32
plie
s =
2 m
m fo
r our
NCF
Power > 1
Power = 1
Power < 1
Advantages of 1- and 2-axis Layup
1-axis layup can be 7 times faster than 4-axis. This advantage can be realized in structures like stringers, shafts, rotors, beams and almost any 1-dimensional
body subjected to combined bend-twist with reduced deformation and vibration
With off-axis plies embedded in bi-angle NCF layer, square corner ply
drops can be made. Time savings at least 40 percent with expected higher
strength and less scrap. Our NCF is best for regular and minimum-gage skins
Traditional 4-axis layup should be re-evaluated: say no to off-axis plies
Tape Laying Efficiency: [0] orientation is 7x faster than off-axis angles
w: 360 in h: 108 in d: 12 in
Safety Factor in Stress and Strain Space
ε1°
ε6° Safety Factor
1.0 1.5
3.0
Safety Factor
1.0
1.5
3.0
OHT OHC Safety and stress concentration factors are equal. OHT and OHC are between 1.5 and 3
Safety factors are not concentric circles as implied by strain = 4 e-3
ε° = 4 e-3
[0/25] NCF
X X’
Stress-based design
Strain-based design
σ1°
σ6° Tool: MicMac-PD
[0/25] [0/±25/0]
[0/45] [0/±45/0]
Anisotropic Orthotropic Isotropic
S > S’ S = S’ F16* ≠ 0 F16* = 0
σ6°
σ1°
σ6°
σ6°
σ6° σ6°
σ1° σ1° σ1°
σ1°
Dassault criterion:
2-axis layup of [0/45] [π/4]
(1-axis layup) (1-axis l’up) (2-axis l’up) Tool: MicMac-PD
FPF Stress Envelopes: σ1° vs σ6° Plane
Anisotropic Orthotropic Isotropic
ε1°
ε1°
ε6° ε6°
[π/4] [0/45] [0/±45/0]
[0/25] [0/±25/0]
ε1°
ε6°
ε6° ε1°
ε1°
ε6°
Equa
l She
ar
Une
qual
She
ar
ε6°
FPF ε = 4 X, X’: S, S’:
X
X’
S > S’
S’ X X’
S
S’ = S
This allowable ε°=4 e-3 is not reliable, and far too conservative
Tool: MicMac-PD
FPF Strain Envelopes: ε1° vs ε6° Plane
Uniaxial Tensile Strength of NCF
1730 MPa [±
12.5
] [0/25]
[0/45]
[±22
.5]
861 MPa
[0/2
5]
718 MPa
661 MPa
[0/4
5]
[0/±25/0]
[0/±45/0] 1097 MPa
815 MPa
1293 MPa
1078 MPa
789 MPa
FPF FPF
FPF FPF
φ φ
Uniaxial tensile strength X, MPa Uniaxial tensile strength X, MPa
LPF LPF
Data
Data
Data
Data 2000 MPa
-Uniaxial Compress: [±φ]16T, [0/±φ/0]8T
[0/±
25/0
]
[0/±
45/0
]
[±] [0/±/0]
[±12
.5]
[±22
.5]
-60 ksi
-120 ksi
-90 ksi
-93 ksi
-Uniaxial comp FPF strength Xi’ MPa -Uniaxial comp FPF strength Xi’ MPa
-X’
Data
Compressive strength is difficult to measure due in part to many different test methods
Data 833 MPa
1120 MPa
Tool: MicMac-Inplane
Data 1120 MPa
Tensile Coupons: w/o & with hole
[0/±25/0] [0/±25/0]/hole
Failure strain = 1.4 percent
X = 1,470 MPa
[±12.5] [±12.5]/hole
Failure strain = 1.1 percent
X = 1,500 MPa
[±22.5] [±22.5]/hole
Failure strain = 1.0 percent X = 611 MPa X = 820
SCF = 1.8 X = 602
SCF = 1.0 X = 864 Mpa
SCF = 1.7
CAI and OHC of NCF KaZak RTM Advaero
HVaRTM
Aldila prepreg
KaZak pultrus’n
[±12.5]16T [±22.5]16T
CAI
OH
C
CAI
OH
C
CAI
OH
C
CAI
OH
C Aluminum honeycomb specimen Impact energy 1,500 in-lbs/in
Hole diameter 0.67”, d/w = 1/6
50 ksi 50 ksi
40 ksi
30 ksi
20 ksi
350 MPa
280 MPa
210 MPa
140 MPa
Tension-Tension Fatigue
Within FPF, no micro cracking
2 plies easier compatibility
[0/25]rT
Variable tows spread thin/thick ≥ 75 gsm
Edge delam suppressed
Homogenized when r ≥ 16
Shear coupling
Strains offset by combined stresses
Deflection and/or rotation managed
Frequency, buckling
improved
1-axis layup [25] pre-plied
7x faster, less error
NCF mass producible
Shallow angle easily done
May change to: [0/20], [0/30], …
Closed-form solutions
Asymmetric, no warpage
Simple ply drop, shape optimized
n.x faster analysis
Better optimized
Faster layup, less error
Strength higher with rectangular spread tows
Optimized ply ≤ h/32
More optimum minimum gage
The Benefits of Bi-Angle NCF
Black Aluminum vs Bi-Angle NCF Black Aluminum
• Symmetric • Balanced • [0p/±45q/90r/. . . ]S
• Integer stacking • Micro crack: tolerated • Heterogenous • Ply drop: a black art • 4-axis layup • Primary plane: σ1 vs σ2
• Fixed strain allowable
Bi-Angle NCF • Asymmetric: simple stack • Unbalanced: anisotropic • [0/φ]16T: easy to match plies • Angle φ: continuous variable • Micro crack: suppressed • Homogenized: toughened • Shape-optimized taper • 1-axis layup: 7x faster • Primary plane: σ1 vs σ6
• Strength ratio: scalable
Strength & Life of Composites Theory of Composites Design Lekhnitskii’s Anisotropic Plates
August 14-23, 2012; online, live, 32-hours of instruction from a teaching staff of 16 Fee of $1,200 includes e-books, software design tools, latest iPad, and composites app All sessions are recorded, downloadable and can be reviewed to fit individual schedule see: http://CompositesDesign.stanford.edu
Composites Design Workshop VII
Free Composites App for iPad
First All-New, All-Free Composites App for iPad
http://compositesdesign.stanford.edu
Background info: Tsai’s Theory of Composites Design
US$ 4.99 (pdf format)
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