Hand layup procedure and effect of holes on composite strength

Paul Peavler

4/22/2010

Outline

Background-motivation

Goals and Objectives-develop hand layup procedure-test effect of holes on composite tensile strength

Methodology-hand layup equipment and procedure -sample preparation and testing

Results, analysis, and discussion-laminate layup-characteristic length of open hole composites

Conclusions-material differences

Motivations

• Hand layup provides a simple, cost-effective composite construction method

1. Use in schools2. Use in small to medium businesses3. One-time applications

• Composites often have holes for fasteners, clearance, or other parts

1. Stress concentration2. Characteristic length3. Varies by laminate properties

Goals and Objectives

• Develop hand layup procedure1. Use on-campus laboratory2. Develop set of instructions3. Make instructions available to students

• Test effect of holes on composite tensile strength

1. Determine tensile strength of modified composites

2. Determine characteristic length

Methodology

Hand layup procedure• Cut prepreg tape into

12”x12” plies, using a [0/45/0/-45/0/45/90/-45]S configuration

• Place laminates on tool with release agent and release film on tool side

• Place perforated release film and bleeder ply above laminate

Fully assembled laminate

Methodology

Hand layup procedure• Enclose tool in vacuum

bag• Use vacuum pump to

remove all air around laminate

• Cure laminate in press• Complex cure cycle

takes approximately 4 hours

Carver heated press

Methodology

Test samples • Cut laminates into test

samples 1, 1.25, and 1.5 inches wide by 10 inches long

• Drill holes of 3/16, 1/4, 5/16, and 3/8 inches

• Apply increasing tensile loads in MTS to test samples until fracture

• Obtain laminate properties from tests of uniaxial layups

Test sample in MTS machine

Results & Analysis

• Material properties• Laminates with only 0 degree and

90 degree plies tested by another student

• Resulted in E1=13.1Msi, E2=1Msi• Values are approximately 1.5x lower

than those provided by Daniel[1]

• Use Daniel text to approximate ν12=0.27 and G12=0.667Msi

• Use program CLT to determine Ex, Ey, νxy, vyx, Gxy laminate properties

• Ex=6.57Msi, Ey=3.81Msi, vxy=0.394, vyx=0.227, Gxy=2.03Msi

[1] Daniel, Isaac M. Engineering mechanics of composite materials. 2nd ed. New York: Oxford UP, 2005. Print.

CLT program

Results & Analysis

• Theoretical failure• Use material properties from

CLT in program LAMFAIL• Predicts first ply failure of

composites; must be modified for ultimate failure

• LAMFAIL predicts ultimate last-ply failure of layup at 9260 lbs/in

• With a laminate thickness of 0.1 in, this results in an unnotched stress of 92.6 ksi

LAMFAIL program

Results & Analysis

• Measured failure and results• Measured failure loads

and resulting stresses are shown at right

• Must correct for plate not of infinite width• Presents K/K∞ factor

• Stress concentrations• Stress concentration

factor for composites cannot be calculated by strength ratio

Width (in)

Hole Size (in)

Max Load 1 (lbs)

Max Load 2 (lbs)

Max Stress 1 (psi)

Max Stress 2 (psi)

1

0.188 5571.2686 5849.9775 54526.19598 57181.177060.250 5008.7554 5287.3491 48715.71934 50890.785980.313   4908.5039   49134.173170.375 4392.7212 4297.4004 42221.46482 43276.9426

1.25

0.188 6798.6235 7524.1182 53273.65085 59874.890180.250 6527.7026 6418.4214 51735.71893 50951.983810.313 6291.9258 5896.4907 49223.73751 47502.925990.375 6134.5381 5618.6167 47915.22311 43603.84227

1.5

0.188 8202.583 8455.9316 55097.48512 57250.721730.250 7938.1162 8154.3813 53781.27507 55072.611540.313 7118.3252 7619.48 48372.318 52073.372430.375 7478.0078 7527.5117 50418.06769 50409.24475

Measured results

xy

xxy

y

x2G

EυEE21K

Stress concentration

wD13w

D12

K

K3

K

K(w)σ)(σ NN

Width correction factor Strength correction

Results & Analysis

• Characteristic length• Based on laminate

properties; dimension over which axial stress averages for failure

• Use Mathcad to solve for δ• Can now easily solve for

characteristic length• Data to right shows all

calculated factors• Average characteristic

length is 0.13387 inches• Approximately 3.4mm

σn1/σ0 σn2/σ0 δ1 δ2 a0_1 a0_2

0.6127219 0.6425564 0.469 0.426 0.1061434 0.12632040.5662749 0.5915581 0.538 0.5 0.107342 0.125

0 0.5981258   0.49   0.16262760.5457216 0.5593638 0.57 0.549 0.1414474 0.15403010.5897767 0.6628571 0.503 0.398 0.0926317 0.14180280.5847738 0.5759152 0.51 0.524 0.120098 0.11354960.5721802 0.5521773 0.529 0.56 0.1391186 0.12276790.5773186 0.5253718 0.521 0.603 0.1723848 0.12344530.6051876 0.6288386 0.48 0.445 0.1015625 0.11692420.5990755 0.6134598 0.489 0.468 0.1306237 0.1420940.5490296 0.5910369 0.565 0.501 0.1202987 0.15562620.5860632 0.5859606 0.508 0.508 0.1815945 0.1815945

Calculated characteristic values

620

N

δ3Kδ2δ1

2

σ

σ

0aR

Rδ

Strength ratio a0 = characteristic length

Results & Analysis

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

σ n/σ

0

Hole Radius, in

1 inch sample data

1 inch sample 2

1 inch sample 1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

σ n/σ

0

Hole Radius, in

1.25 inch sample data

1.25 inch sample 1

1.25 inch sample 2

Results & Analysis

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

σ n/σ

0

Hole Radius, in

1.5 inch sample data

1.5 inch sample 1

1.5 inch sample 2

Results & Analysis

Conclusions

• Material properties• Material is approximately

1.5x weaker than typical unidirectional carbon fiber

• Stress concentration factor and strength ratio• Stress concentration factor

is 3.25; strength ratio is approximately 0.54

• Characteristic length is 0.13387 inches• This is approximately 1.5x

lower than bookvalue of 5 mm with different layup

Failed test sample

Recommended future work

• Complete hand layup video• Video was captured of the hand layup process• This video can be edited and used as a guide for

future student projects and classes• Test different layups

• Find characteristic length for various layups of same material

• Test different materials• Test material with strengths closer to that of the

general textbook values• Determine how much of an effect strength has on

concentration factor and characteristic length

Questions?

Appendix

Appendix

Appendix

Appendix

AppendixSegment Force Dwell Time Temp SP 1 Temp SP 2

1 4300 lb 5.2 min 96 °F 96 °F

2 4300 lb 5.3 min 122 °F 122 °F

3 4300 lb 5.2 min 149 °F 149 °F

4 4300 lb 5.3 min 175 °F 175 °F

5 4300 lb 5 min 175 °F 175 °F

6 4300 lb 5 min 175 °F 175 °F

7 4300 lb 5 min 175 °F 175 °F

8 4300 lb 5 min 175 °F 175 °F

9 4300 lb 3.7 min 194 °F 194 °F

10 4300 lb 3.8 min 212 °F 212 °F

11 4300 lb 3.7 min 231 °F 231 °F

12 4300 lb 3.8 min 250 °F 250 °F

13 4300 lb 22.5 min 250 °F 250 °F

14 4300 lb 22.5 min 250 °F 250 °F

15 4300 lb 22.5 min 250 °F 250 °F

16 4300 lb 22.5 min 250 °F 250 °F

17 4300 lb 15 min 60 °F 60 °F

18 4300 lb 15 min 60 °F 60 °F

19 4300 lb 15 min 60 °F 60 °F

20 4300 lb 15 min 60 °F 60 °F

Cure cycle

Appendix

Sample 1 width (in) Sample 1 thickness (in) Sample 2 width (in) Sample 2 thickness (in)

0.992 0.103 1.003 0.102

1.008 0.102 0.999 0.104

1.002 0.102 0.999 0.100

1.020 0.102 0.993 0.100

1.239 0.103 1.232 0.102

1.237 0.102 1.235 0.102

1.241 0.103 1.229 0.101

1.243 0.103 1.239 0.104

1.474 0.101 1.477 0.1

1.476 0.1 1.466 0.101

1.457 0.101 1.478 0.099

1.44 0.103 1.464 0.102

Measured sample dimensions

Appendix

K/K∞ σn1(∞) σn2(∞)

1.0405649 56738.046 59500.726

1.0763889 52437.059 54778.277

1.1272491 0 55386.45

1.196875 50533.816 51797.091

1.0251471 54613.326 61380.568

1.0466667 54150.052 53329.743

1.0763889 52983.884 51131.622

1.1157143 53459.699 48649.43

1.0171131 56040.374 58230.459

1.0314815 55474.389 56806.379

1.0510173 50840.143 54730.015

1.0763889 54269.448 54259.951

Finite width corrections and stresses