edam meeting template v2

8/2/2019 Edam Meeting Template v2

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Optimization of composite bonded joints andrepairs

Maria Victoria Castro FernndezEDAM focus area (MIT-Portugal)Faculty of Engineering, University of Porto

Supervisor: Marcelo Moura

Co-Supervisors: Antonio Torres Marques, Lucas Silva, Thomas Eager& Manuel Freitas

EDAM Meeting FEUP

Porto, March 16, 2011


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Objectives

The use of fracture mechanics in designing againstdamage propagation;

Create methodologies to conduct bonded

joints/repairs in structures of compositesmaterials;

Development of systems to teach technicians and

shop-floor workers how to optimize the costs andbonding performance in structures currently used

in industry.


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Assessed Needs

Better understanding of bonded

joints behavior, to develop anindustry with enough knowledge

to design structures;

Impact of the repairs and qualitycontrol in the durability of the

blades;

Critical costs when a wind turbinehas stop for maintenance.


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Main Tasks

Fatigue characterization of bonded joints

Evaluation of geometrical changes effects on

bonds fatigue strength

Cost analysis

Manufacture

Non-destructive testing

Durability

Methodology Development


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Time-line of the main tasks


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FATIGUE CHARACTERIZATION


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Main Tasks

Fatigue characterization of bonded joints undermode I, mode II and mixed-mode loading:

Mode I: DCB (Double Cantilever Beam)

Mode II: ENF (End Notched Flexure)

3 points Mixed mode: still define the possible test

ELS-MM End Loaded Split for Mixed-Mode;

SLB (Single-Leg Bending).

Variables: Determination of Paris law parameters

and fracture surfaces characterization.


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Introduction

Cyclical fatigue loading leads to failure even at small loads.

For fatigue damage two approaches have been used extensively - stress-life andfatigue crack growth (FCG).

The FCG method is the correlation between the rate of fatigue crack growth per

cycle (da/dN) and the change of one fracture parameter (G Energy Release

Rate) over the time.

The Paris-Law is an empirical law.

2

1

C

I

Ic

GdaC

dN G

Paris-Law


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Experimental tests

The ASTM E 647 08 standard was used

The tests were made with load control (constant

amplitude loading).

The load ratio (R) is 0.1 and the maximum load is50% of the average maximum static load.

The main objective of these tests is to define the

fatigue crack growth rate as a function of the

(Gmax/Gic (i=I,II))


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)1(' 2

aa

E

EE

E

tha '634

2

222

)1(22

bEI

aP

da

dC

b

PG

I

Data reduction scheme to evaluate GI =f(ae)

Pirondismethod:

CBBM:

2 3

1 2 3 4C A A a A a A a

da

dC

b

PG

I

2

2

ef ( )a C

32

3

2221

'

2aaa

bE

t

PC

a

Polynomial:


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Experimental tests

Double Cantilever Beam

End-Notched Flexure

Both tests have equivalent dimensions,

because the Paris-law depends on the

specimen geometry.


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Specimens

DCB

L = 125 mm

a0 = 45 mm b= 25 mm

l3= 15 mm

h = 2.7 mm

ENF

L = 125 mm

a0

= 45 mm

b= 25 mm

h = 2.7 mm

The adhesive thickness is 0.2 mm


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DCB Results

y = 0.0156x2.9155R = 0.9446

0.0001

0.001

0.01

0.1 1

dae/dN

GImax/GIc

dae/dN

Power(dae/dN)

100

150

200

250

300

350

400

40 50 60 70 80

G

Imax

(J/mm2)

a (mm)

G CBBM

GmaxPirondi

40

80

120

1000 11000 21000 31000

a(

mm)

N (nmero de ciclos)

ae

a medido

0.0005

0.005

0.2

da/d

N

GImax/GIc

da/dN (Pirondi)

dae/dN (CBBM)


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DCB Results

Ysec = 0,0196x3,2675R = 0,6644

Ypol = 0,0055x2,29R = 0,8019

0.0001

0.001

0.010.2

dae

/dN

GImax/GIc

Lei Geral (secante)

Lei Geral (pol)

Power (Lei Geral(secante))

Power (Lei Geral(pol))

General Law 0,0055 2,29Polynomial Method

2

1

C

I

Ic

GdaC

dN G

General Law 0.0196 3.26747Secant Method

Paris law constants

C1 C2

1 0.0255 3.2702

2 0.0156 2.9155

3 0.1226 5.0217

4 0.1837 4.9585

5 0.0163 3.62376 0.014 2.7019

C1 C2

1 0,0078 2,3391

2 0,0048 2,161

3 0,0059 2,4042

40,0063 2,0792

5 0,007 3,0529


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ENF Results

A Matlab program was made to calculate the

displacement, the load and the compliance of the

specimen by using the real time acquisition data

of the MTS machine.


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ENF Results

0

0.5

1

1.5

2

2.5

3

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0 50000 100000 150000

G

ii

C

N (Number of Cycles)

C

G CBBM

-1200

-1000

-800

-600

-400

-200

049 49.5 50 50.5 51 51.5 52 52.5

Load(N)

Time (s)

y = 0.0686x2.9697R = 0.6022

y = 0.2242x3.804R = 0.7765

y = 0.0344x3.0875R = 0.8856

0.00001

0.0001

0.001

0.01

0.1

11.00E-01 1.00E+00

dae/dN

Giimax/Giic

Specimen 1

Specimen 2

Spec. 1 Pol. Method

Power (Specimen 1)

Power (Specimen 2)

Power (Spec. 1 Pol.Method)


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INTRODUCTION TO THE WINDINDUSTRY


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Wind Industry

There some projects to develop more efficient methods to

build the eolic blades.The demand for blades has become larger in the last

years.


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Blades

1

2

3


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BLADES

All the structure is bonded.

The adhesive joints are critical points in the bladestructure;

The repairs are performed by bonding patches

Fatigue behavior is crucial in these structures


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COSTS ANALYSIS


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Manufacturing

Manufacturing costs and weight saving:

In 8 ton, 1 ton approximately is from the adhesive.

Durability:

Less maintenance of the blades in situ.

Quality of the bonded joints:

Infrared (IR) scanning

Ultrasounds


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Manufacture

i) Make an impact evaluation of the adhesive cost in the

cost of the blade Variables: costs involved in manufacturing the blade and costs

involved in the bonding.

ii) Optimization of the bonding process by reducing the

time, raw materials and costs

Variables: Time of bonding and amount of adhesive used.

iii) Quantify the costs reduction and the impact in the

cost of the blade Variables: costs related to the improvements proposed in ii).


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Non-Destructive testing

Define the most appropriate methodology for the

quality control of the blades, the costs ofimplementing this technology and the

advantages.

Variables: most important parameters, costs ofimplementing the selected technology and the main

advantages.

Possible methodologies to define the technology:

SWOT analysis

Weight matrix for the most important parameters.


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Methodology Development

Develop a cost-effective bonded process for

implementation in the wind energy industry.

Variables: create a methodology to manufacture blades with

optimized bonded joints.


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Conclusions

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