lightweighting with composites, adhesive properties … · 4 ashland specialty ingredients adam...

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Ashland Specialty Ingredients

Lightweighting With Composites, Adhesive Properties

and Initial Bond Line Read Through Measurements

Michael J. Barker Adam Burley

Ashland Inc. Continental Structural Plastics, Inc.

Society Plastics Engineers, Automotive Composites Conference & Exhibition

September 7-9, 2016

Detroit, Michigan

Ashland Specialty Ingredients, Commercial Unit of Ashland Inc.

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Michael J. Barker

Michael Barker earned his graduate degree

in Chemistry from the University of Detroit

where he specialized in rubber toughening of

thermoplastics. He continued with post-

graduate study at the University of Washington

in the area of carbon fiber composite

technology and protective surface coatings.

For over 30 years he has specialized in

structural adhesive and coatings research for

the aerospace and automotive industries

holding rolls of increasing responsibility at

General Motors Research, BFGoodrich R&D

and Ashland Inc. He has been with Ashland

Inc. for 15 years where he has held positions in

R&D and research management and is

currently a Research Fellow in their Structural

Adhesive group. While at Ashland he has

earned four US patents for structural adhesive

technology including two for epoxies and two

for polyurethanes.

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Adam Burley, Ph.D.

Dr. Burley graduated with a B.S. in Chemical and

Biomolecular Engineering from The Ohio State University in

2006. He graduated with M.S. and Ph.D. degrees in Chemical

and Biomolecular Engineering, also from The Ohio State

University, in 2012. His dissertation was on improving the

fundamental understanding of bubble nucleation in polymer

foaming. Dr. Burley has currently been a Senior Materials

Scientist at Continental Structural Plastics for the last four

years. He has specialized in new material and process

development with particular emphasis on carbon fiber; heat

transfer applications; and surface and adhesive appearance

improvements.


Abstract

Regulations mandating improved automotive fuel efficiency and reduced carbon emissions have

accelerated the need for lighter weight vehicles. The resultant use of thinner gage composites for exterior

body panels to achieve weight reduction has put renewed focus on the need to understand the causes

and mitigation of adhesive bond line read through, BLRT. This study will review the fundamental needs

for a successful adhesive bonded composite program such as heat resistance and fast cure with

emphasis on reducing bond line read through. Finite element analysis is used to create a supporting role

in predicting key areas to focus and assist in generating a mathematical model. A new tool will be

introduced to measure bond line read through of non-painted surfaces and several key constitutive

properties such as adhesive elongation, modulus, coefficient of thermal expansion and cure time will be

examined through formula and process manipulation for their respective contributions to mitigate surface

deformation.

This paper will review the basics of bond line read through of composite surfaces, generate an FEA

model for direction of focus and examine adhesive constitutive properties for their ability to mitigate

adhesive related surface defects.

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Outline

• Shifting Requirements in Composite Bonding

– Lightweighting

• Bond Line Read Through, (BLRT)

• Search for Technical Solutions

– FEA Analysis

– Surface Defect Measurement

– Model Adhesives

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Shifting Requirements in Composite

Bonding

• Regulations driving the need to improve fuel efficiency and reduce

carbon emissions have increased need for weight reduction

– Increased focus on:

• Glass and carbon filled composites

• Dissimilar Materials

– Technology Enablers

• Improved economics

• Thinner gage/ lighter weight

• Reduced cycle times i.e. faster cure

• Ecoat oven stable system

• Eliminate need to hide bond lines, allowing for more structure and

further light weighting”

• Improved “first time” surface appearance

Reduced BLRT

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Framework

• Goal:

– Weight Reduction Through Use of Adhesive Bonded Composite

– Successfully Compete Against Existing Substrates for Exterior Body

Panel Business

• Outcomes:

1. Ecoat Oven Resistant Composite and Adhesive: 204C

• Assembly Prior to Ecoat Application

2. Fast Cure Adhesive: 90 – 120 Sec

• Improve Economics

3. Eliminate Bond Line Read Through

• Reduce Rework/ Cost

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Heat Resistance at 204C “The First Hurdle”

“An Adhesive with Good Strength Build and BLRT that Can

Not Survive Heat Requirements Will Not be Successful”

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Lap Shear Preparation

• All SMC 1.8 mm bonded to SMC 2.5 mm

• Cure 90 Seconds at 127C

• Bond Gap 0.76 mm

• 25.4 mm Overlap

• Crosshead 12.7 mm/ min

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• Lap Shear Requirement is

0.3 Mpa

• 120 Min Used as Safety

Factor

• All but PUR2, H5, EP1

Passed Heat Requirements

• Best Five Pulled Forward

• Best Case Formulas

Evaluated Vs. Temperature

• All Pass Lap Shear

Requirements

• No Post Bake Data Shown

As Control

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IDTensile,

Mpa

Young's

Modulus,

Mpa

% ElongPoisson's

Ratio

CLTE,

-30-0C,

µm/m°C

CLTE,

100-130C,

µm/m°C

H1 32 1760 11 0.344 87 268

H2 22 680 73 0.462 72 255

H3 26 1490 22 0.351 79 275

H4 25 1320 29 0.378 70 252

Ep2 36 3020 2 0.370 65 207

Bulk Mechanical Properties of Key

Formulas

• Young’s Modulus and Elongation Vary from High to Low • Tensile Rises with Modulus

• T ensile Drops with % Elongation

• % Elongation Drops with Modulus

• No Relationship with Poisson’s Ratio or CLTE

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Reactivity/ Strength Build

Cross Peel Tester

“The Second Hurdle”

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ID Working

Time, min Strength 90 Sec at 127C, SMC, Mpa

H1 14 0.8

H2 8 0.5

H3 12 0.6

H4 10 1.0

Ep2 60 1.0

• Strength Build Over SMC

• Green Strength Defined at 0.3 to 0.7 MPa Depending on Weight of Part

and Area of Adhesive

• Good Strength Production Within 90 Seconds for All Systems

• Improved with Higher Modulus

• Lower Modulus Adhesive Yields Less Strength than Other Adhesives

• Likely Result of Reduced Cross Link Density

• All Systems Exceed Working Time Goal of 8 Minutes

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Bond Line Read Through “The Most Difficult Hurdle”

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Bond Line Read Through is Defined as

Transference of the Cured Adhesive Path

Showing Through the Class A Surface

BLRT is a Complex Phenomenon Which Will Require

a Multifaceted Solution- Not One Simple “Fix”

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BLRT in the Literature

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Primary Factors Creating BLRT

• Differential CLTE Adhesive and Substrate

– Zero State Considerations

• Bond Line Squeeze Out

– Thickness of Adhesive Bond Gap Plays Significant Roll

• Net Out

– May Cause Excessive Squeeze Out

– Transference of Hit Area into Bond Line

• Bond Line Stand Offs

– Standoffs May Telescope Through to Show Surface

• Differential Substrate Thickness

– Variation in Heat and Cooling Rates Relative to State of Adhesive

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Secondary Factors Creating BLRT

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• Bond Gap Uniformity

– Consistency of part thickness

– Consistency of part dimensions

– Fixture repeatability

• Bond Flange

– Width – must be capable of maintaining adhesive foot print

• Minimize squeeze Out

• Bead placement Robotic programming

Adhesive dispense consistency

• Shrink of Adhesive Due to Cure – Typically a Fraction of Change Due to CLTE


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• Inners & Outers Need to be Mated in a Stress Free State

– Part warping needs to be minimized

– Use of fixtures as a dimensional control device must be eliminated

• Fixture Temperature

– Uniform Rates of Change Inner and Outer

• Heat and Cool

• Post Bake Temperatures

– Uniform Rates of Change with both Substrate Sides

– Lower Temperatures Preferred

Mixed Bag of Variables Contributing to BLRT

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Literature Solutions to BLRT

• Reduce Adhesive Modulus

• Increase Adhesive Elongation

• Reduce Bond Gap Thickness

• Reduce Fixture Cure Temperature

• Reduce Post Bake Temperature

ID

Tensile,

Mpa

Young's

Modulus,

Mpa

% ElongPoisson's

Ratio

CLTE,

-30-0C,

µm/m°C

CLTE,

100-130C,

µm/m°C

H1 32 1760 11 0.344 87 268

H2 22 680 73 0.462 72 255

H3 26 1490 22 0.351 79 275

H4 25 1320 29 0.378 70 252

Ep2 36 3020 2 0.370 65 207

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BLRT Sample Preparation

25 cm

25 cm

• 25 cm x 25 cm Panels

• 1.8 mm Class A x 2.5 mm Structural SMC

• 9 Inch Bead of Adhesive Down Center

• Fixture Cure at 127C

– On Stops to Control Gap

– Vary Adhesive Thickness

– Vary Bead Width

• Post Bake 40 Minutes at 204C

• Testing Within 16 Hours

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FEA Model

• Geometry

• FEA study: ¼ - symmetry model

• Adhesive, CLTE, Modulus, Bond Gap Varied

• Z-displacement data extracted at the path on the edge of the top panel up to 20mm

from symmetry plane

• The slope (1st derivative) and curvature (2nd derivative) for this path are calculated

and evaluated

Symmetrical Structure, ¼ Part Modeled

ANSYS-Mechanical® used to study adhesive properties on panel surface

curvatures

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Effects of Adhesive Properties on BLRT

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• The curvature model has 4 key features:

– It is linear in the effect for CLTE.

– It is asymptotic in the Bond Line thickness with an exponential rise.

– It is asymptotic in the Modulus with an exponential rise.

– The Curvature is 0 when any of the 3 factors (CLTE, Bondline or Modulus) are 0

• Model Requires SMC, Process and Design Variable to be Functional

ModulusMBondlineB XX

CLTE eeXburvature

11*C

Mathematical Model of FEA Results

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• TMA Measurements

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5.93min

-4.633µm-0.1955%

43.41min

20

40

60

80

100

Tem

pera

ture

(°C

)

-10

0

10

20

30

40

Dim

ensio

n C

hange (

µm

)

0 10 20 30 40 50

Time (min)

Sample: 9100 FC RT 93 shrinkage #2Size: 2.3695 mmMethod: Pliogrip shrinkage 93CComment: Q400 TMA, 50mL/min N2, macroexpansion probe

TMAFile: Q:...\Thermal\Data\Q400\78852-01tm.012Operator: tabRun Date: 14-Oct-2013 15:35Instrument: TMA Q400 V22.5 Build 31

Universal V4.5A TA Instruments

Expansion/

Contraction Due to

Thermal Variation

Shrinkage

Due to

Chemical

Reaction

Irreversible Thermodynamic Events Results in Permanent Deformation

Temperature

Profile

Dimension

Change Profile

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Irreversible Thermodynamic Events

Percent Cure of Adhesive and Composite Prior to Post Bake

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Measurement of Bond Line Read Through

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Steinbichler ABISoptimizer

• Based on Speckle-Shearing,

Phase- Shifting1 and Algorithms

Reproducing Different Sized

Grinding Stones, the Part Surface

is Mathematically Generated

• From the Math Data a Single

Profilometer Line is Generated

Creating an Altitude Measurement

• The Altitude Measurements are

Converted to their Second

Derivative to Emphasize Change

in Slope i.e. Curvature 2

• The Maximum Curvature for Each

Line is Recorded for Comparison

1 US Patent 5,493,398

2 R. Hsakou, JEC Composites Magazine, 23,

March 2006, pp105-108.

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Gage R & R Analysis

• Power is the Probability the Correct

Decision will be Made- 80% Preferred

• Difference of 10 Microns Requires 6

Panels

• Difference of 25 Microns Requires 2

Panels

• Precision of Equipment is 10 Microns

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Laboratory Results

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• 4 of 5 Formulas Demonstrate Less BLRT

on Thicker Structural Composite

• Effective Method of Minimizing BLRT

• Differences Between Formulas Difficult to

Resolve

• Measurement Standard Deviation

Larger than Expected

• BLRT Not Consistent Across Panels

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H4

H3

H2

H1

Ep2

0.80.70.60.50.40.30.20.10.0

P-Value 0.620

P-Value 0.656

Multiple Comparisons

Levene’s Test

ID 2

min

Test for Equal Variances: Thin vs ID 2 minMultiple comparison intervals for the standard deviation, α = 0.05

If intervals do not overlap, the corresponding stdevs are significantly different.

18001600140012001000800600

0.80

0.75

0.70

0.65

S 0.0244563

R-Sq 89.7%

R-Sq(adj) 84.6%

Young's Modulus, (MPa)

Ave. C

urv

atu

re, (/

m)

Regression Plot, Curvature Vs. Modulus, 2 Min. @127C, Thin, PB, 0.76mm Gap

Ave Cur Thin = 0.5544 + 0.000129 Y Mod

P = .053

• Overlay of Post Baked Non-

bonded SMC

• Difference Between Formulas is

Less than std of Measurements

Thus Can’t Resolve w/o Much

Larger Sample Size

• Test for Equal Variance Indicates

Samples are Not Significantly

Different

• Regression Plot Vs. Young’s

Modulus Gives Good Correlation

with P = 0.053, (Strongly

Influenced by One Adhesive)

• Trend Similar to FEA

• Optimized with Reduced Modulus

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5 Min

4 Min

3 Min

2 Min

1.5 Min

1 Min

0.70.60.50.40.30.20.10.0

P-Value 0.465

P-Value 0.367


Levene’s Test

ID

Test for Equal Variances: Data vs IDMultiple comparison intervals for the standard deviation, α = 0.05


54321

0.75

0.70

0.65

0.60

0.55

0.50

S 0.0317516

R-Sq 88.8%

R-Sq(adj) 85.1%

Time2

H2

Mean

Regression Plot: H2 Vs. Cure Time at 127C, .76mm Bond Gap, Thin, PBH2 Mean = 0.4812 + 0.05420 Time2

P = .016

• Overlay of Post Baked Non-

bonded SMC



Different

• With Removal of 1 Min Cure Data,

Regression Plot Vs. Cure Time

Gives Good Correlation with P =

0.016

• Optimized with Minimum Cure

Time, (Down to 90 Sec)

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1.11.00.90.80.70.60.50.4

3.0

2.5

2.0

1.5

1.0

0.5

0.0

S 0.414082

R-Sq 91.3%

R-Sq(adj) 86.9%

Ave. Curvature, (/m)

Ad

hesi

ve B

on

d G

ap

, (m

m)

Regression Plot, H2 Vs. Bond Gap, 2 Min at 127C, Thin Side, PBGap 2 = - 1.689 + 4.235 Curv3

P = .045

3.00

1.52

0.76

0.43

0.50.40.30.20.1

P-Value 0.490

P-Value 0.799


Levene’s Test

Gap

Test for Equal Variances: H2, Curvature vs GapMultiple comparison intervals for the standard deviation, α = 0.05


• Formulas Vs. Bond Gap

• Curvature Increases with Gap



Different

• Regression Plot Vs. Bond Gap

Gives Good Correlation with P =

0.045

• Optimized with Minimum Bond

Gap

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40353025201510

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.50

S 0.110221

R-Sq 75.4%

R-Sq(adj) 50.8%

ByVar1

Mean

1

Regression Plot, Curvature Vs. Bead Width, H2, 90 Seconds at 127C, PBMean1 = 0.4057 + 0.01058 ByVar1

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20

13

0.60.50.40.30.20.10.0

P-Value 0.344

P-Value 0.462


Levene’s Test

Wid

th

Test for Equal Variances: H2 Curvature vs WidthMultiple comparison intervals for the standard deviation, α = 0.05


• H2 Vs. Bond Width



Different

• Regression Plot Vs. Bond Width

Yields Poor Correlation, with P =

0.331

• No Significant Relationship

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• H2 Vs. Bond Gap With and

Without Post Bake

• Main Effects Plot Confirms Post

Bake Degrades Curvature

• Optimize With Thin Bond Gap

and No Post Bake

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General Summary

• Through FEA a Mathematical Model Has Been Created to

Identify Key Focus Areas to Mitigate BLRT

• New Hybrid Adhesives Have Been Created and are Able

to Withstand 204C for 120 Minutes

• Young’s Modulus and Elongation Have Been Adjusted

and Optimized to Minimize Bond Line Read Through

• Lower Modulus Adhesives May Have Arrested Strength

Build Over SMC

• Working Times ≥ 8 Minutes and Strength Builds Within 90

to 120 Seconds Have Been Obtained

• A New Tool for Measuring BLRT Prior to Paint Operation

Has Been Introduced

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Curvature Measurement Summary

• Overlaying Non-bonded Composite Curvature Shows Difference

Between Formulas Are Less than Standard Deviation of

Measurements. Thus Exact Resolution Will Require Much Larger

Sample Size

• Thicker Side of Thin/ Thick Assembly Exhibits Less Curvature and is

an Option to Reduce BLRT

• Regression Plot of Curvature Vs. Young’s Modulus Showed Good

Correlation. Trend Similar to FEA Showing Formula Area to Focus

• Regression Plot Curvature Vs. Cure Time Shows Good Correlation

With 90 Second Fixture Time Showing Best Results

• Regression Plot Curvature Vs. Bead Width Was Not Significant

• Regression Plot Curvature Vs. Adhesive Thickness Showed Good

Correlation and Optimized With Minimum Bond Gap

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Future Work

• Complete Statistical DOE Around Adhesive

Modulus, Cure Time and Curative Package to

Optimize Heat Resistance, Rate of Cure and

Reduction in Bond Line Read Through

• Commercialize Adhesive Technology in Fall of

2016

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Ashland Specialty Ingredients Ashland Specialty Ingredients

Disclaimer The information contained in this presentation and the various products described are intended for use only by persons

having technical skill and at their own discretion and risk after they have performed necessary technical investigations, tests

and evaluations of the products and their uses. This material is for informational purposes only and describes the scientific

support for the use of the products described herein as an ingredient in cosmetic products intended to enhance appearance

and other cosmetic benefits or to enhance performance of an end product. Certain end uses of these products may be

regulated pursuant to rules governing medical devices or other regulations governing drug uses. It is the

purchaser’s responsibility to determine the applicability of such regulations to its products. While the information

herein is believed to be reliable, we do not guarantee its accuracy and a purchaser must make its own determination of a

product’s suitability for purchaser’s use, for the protection of the environment, and for the health and safety of its

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Neither Ashland nor its affiliates shall be responsible for the use of this information, or of any product, method, formulation, or

apparatus described in this brochure. Nothing herein waives any of Ashland’s or its affiliates’ conditions of sale, and no

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The testing information (the “Testing Information”) has been gratuitously provided by Ashland. The Testing Information is

based on many factors beyond Ashland’s control, including but not limited to, the conditions prevailing when the testing was

conducted, and in some cases, is based on data generated with development samples of the Active Ingredient. Although it is

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party. You may not make commercial use of the Testing Information, or make claims with respect to your products based the

Testing Information, without the written agreement with Ashland covering such use.

® Registered trademark, Ashland or its subsidiaries, registered in various countries

™ Trademark, Ashland or its subsidiaries, registered in various countries

* Trademark owned by a third party

© 2015, Ashland

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EP2 2 min + PB

H2 2 min + PB

• EP2 and H2 Raw

Data from

Steinbichler

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