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

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