research presentation of brandtner-hafner fracture analytics at in-adhesives symposium 2017

INTERFACE FRACTURE BEHAVIOUR

OF INDUSTRIAL ADHESIVES:

A NOVEL EVALUATION APPROACH

FOR ADHESIVE SELECTION

by

Symposium on Innovations in

Adhesives and their Applications

Munich, Germany,

February 14-15, 2017

Dr. Martin BRANDTNER-HAFNER

Introduction• Look at the schematical structure of a bonding

• You will find different sections with various properties

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Source: Habenicht (2005)

Introduction• Look at the schematical structure of a bonding

• You will find different sections with various properties

• There, the interface is the „weak spot“

3

Source: Habenicht (2005)

Introduction• If a crack appears, it is essential how it turns out.

• Six different „Failure Modes“ may occur:

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Source: ASTM D5575 (2006)

Source: Habenicht (2005)

Mechanical Testing of Adhesive Composites

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Mechanical Testing of Adhesive Composites

Source: Habenicht (2005)

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Limitations of Mechanical Testing

• Testing of BONDING ≠ Testing of CRACKING

• Based upon Continuummechanics, NOT Fracture Mechanics

• Just ONE PARAMETER is used to rate

the safety of the WHOLE STRUCTURE (i.e. „Strength“)

• No Statements about Cracking Behaviour possible

• Standardised testing often limits „Thinking Beyond“.

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Fracture Mechanical Considerations

Crack Opening Modes

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Source: Brandtner-Hafner (2016)

Type Loading Condition Cracking Condition

Mode I Tensile, Bending Crack opening

Mode II Biaxial – Tensile/ Pressure In-Plane Shearing

Mode III Torsion Cross-Plane Shearing (Tearing)

Fracture Mechanical Considerations

Source: Brandtner-Hafner (2016)

Fracture Prozess Zones

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Fracture Mechanical Considerations

Source: Brandtner-Hafner (2016)

Fracture Prozess Zones

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Fracture Mechanical Considerations

Source: Brandtner-Hafner (2016)

Fracture Prozess Zones

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Fracture process gets more complex when

there are different bonding partners.

Fracture Mechanical Considerations

Fracture Stability Conditions

Source: Brandtner-Hafner (2016)

Type Fracture Condition

A unstable

B semi-stable

C stable

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Fracture Mechanical Considerations

Fracture Stability Conditions

Source: Brandtner-Hafner (2016)

Type Fracture Condition

A unstable

B semi-stable

C stable

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„running crack“

„controlled crack“

total failure

limited failure

Fracture Mechanical Considerations

Fracture Stability Conditions

Source: Brandtner-Hafner (2016)

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Type Fracture Condition

A unstable

B semi-stable

C stable

Experimental Investigations

Adhesive Candidates for Fracture Mechanical Testing:

Name Chemical Basis

A Acrylate 1K

B MS-Polymer 1K

C Polyurethane 2K

D Acrylonitrile 1K

E Polyurethane 1K

F Polyurethane 1K

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Results

Source: Brandtner-Hafner (2016)

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Results

Source: Brandtner-Hafner (2016)

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Opposing Correlation between

„STRENGTH“ & „RESISTANCE“

Results

Source: Brandtner-Hafner (2016)

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Results

Source: Brandtner-Hafner (2016)

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Results

Source: Brandtner-Hafner (2016)

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Colour = „Fracture CONDITION“

Size = „Fracture RESISTANCE“

Results

Source: Brandtner-Hafner (2016)

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Colour = „Fracture CONDITION“

Size = „Fracture RESISTANCE“

E & F are the right choice!

Concluding Remarks

1. Use adhesives showing maximum fracture resistance:

i.e. PU-1K for bonding wood.

2. Avoid adhesive systems tending to crack unstable:

i.e. they are too brittle → low fracture toughness.

3. Do not rely on just one engineering parameter alone

when considering adhesives for your application.

i.e. tensile strength, peel strength, elastic modulus,...

4. Do not rely just on engineering standards alone

when choosing the best-fitting adhesive system.

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Thank you!Dr. Martin Brandtner-Hafner

Fracture Mechanics Professional

E-Mail: info@brandtnerhafner.com · Web: www.brandtnerhafner.com