the importance of bonding an historic overview and future possibilities · 2016. 4. 14. · general...

FRP strengthening for flexure

The Importance of Bonding – An Historic Overview

and Future Possibilities

by

Professor Björn Täljsten

Luleå University of Technology

Sto Scandinavia AB

Sweden


Outline

• Introduction • Ancient times • Industries/Medicine/Sport • Building Industry • Theory • Future Possibilities • Conclusions • Acknowledgement


Introduction

Adhesion: The state at which two surfaces are held

together by interfacial forces, which may consist of all

known chemical attractive forces, as well as mechanical

interlocking action or both.

Adhesive: A substance capable of holding materials

together in a functional manner by surface attachment

(performance). A general term that includes cement, glue,

mucilage and paste.

Bond between materials is essential and

has a long history


History 36 000 years ago: Bitumen

4000 BC: Tree sap, tar

1500-1000 BC: Beeswax, egg white

1700 A.D: Animal and fish glues

1750 A.D: Casein

1910 A.D: Bakelite

1930 A.D: Epoxies Making of and adhesive, Ancient Egypt


History

Animal Skin Glue is made from animal's skin or bone and it has been used as adhesive

from ancient times. For art material, Rabbit's, sheep's or deer's skin glue are popular.

In western painting, animal skin glue had been one of important binder until late medieval

times, like egg, or Gum a. Especially it had been used for manuscripts. Today, we use it for

only size or ground. In eastern painting, animal skin glue is still used as the most important

binder.

Shattered rabbit skin glue Sanzenbon

(Japanese art material)


Adhesive Materials can be classified in a number of ways:

• Natural or synthetic polymer base;

• Thermoplastic or thermosets;

• Physical form (one or multiple component, films, etc)

• Functional type (structural, hot melt, pressure sensitive;

• Chemical families (epoxy, silicone, etc.)

Introduction


Adhesives - Classification

Introduction

Adhesive

Organic

Natural

Non-Organic

Synthetic Cements Silicates Ceramic

Animal

Vegetable

Mineral

Natural Rubber

Epoxy

Polyurethane

Phenol

Polyester

Vinyl ester

Acrylics

Melt adhesives.

etc.


General Considerations in the Application of Adhesive Bonding

• When applied adhesives have to 'wet' the surface;

• They need to be mobile and flow into all the tiny nooks and crannies

of the substrate;

• If the adhesive does not wet the substrate well, poor adhesion is

likely to be a result;

• Once good wetting takes place, an adhesive needs to become solid

and not flow at all. This is called setting or curing (polymerization);

and,

• Positional indication (imaging).

Introduction


Surface Free-Energy Exchange

If the surface tension value of the liquid is greater than the surface-

free energy value of the substrate the liquid molecules stay bound

together

Poor wetting means a poor bond!

Introduction


Surface Free-Energy Exchange

When the surface free energy value of the substrate is higher than

that of the liquid it allows the liquid to uniformly wet the surface

This is important to achieving a good bond

Introduction

Good Wetting

Bad Wetting


Adhesive Joints

Breaking strength is determined by:

• Mechanical properties of the materials of the joint;

• The extent of the interfacial contact (number, extent, type and

distribution of voids);

• Presence of internal stresses;

• The joint geometry; and,

• The details of mechanical loading.

Introduction


Bonding Mechanisms

• Mechanical Interlocking;

• Formation of covalent bonds across the interface;

• Electrostatic Attraction-dominant

Introduction


Surface Treatment

• No treatment (low cost poor reproducibility);

• Solvent wiping;

• Vapor degreasing;

• Mechanical abrasion;

• Plasma treatment;

• Etching;

• Chemical deposition-primers, organosilanes

Introduction


Modes of Failure

• Adhesion failure

A uniform stress pattern in an adhesive joint is seldom produced by

the application of external force.

Introduction

• Structural failure

• Cohesive failure


Loads on Adhesive Bonded Joints

Tension Compression

Shear

Cleavage Peel

Both parts are rigid One or both parts are flexible

Introduction


Benefits of Adhesives

• Joins dissimilar materials

• Even stress distribution

• Fills large gaps

• Seals and bonds

• Easily automated

• Aesthetically acceptable

Introduction


Automotive/Railway and Aerospace Industries General motivation for adhesive structural bonding

Lightweight construction: Adhesives improve the stiffness and

strengths of bonds. Therefore the weight of structures and car-bodies

can be reduced.

Mixed Materials: Realization of structural bonding concepts of

different substrates (FRP, metals, glasses, ceramics etc.)

Crash performance: Improvements are possible by the use of

substrates and adhesives with a high potential of energy absorption

Long time performance: Adhesives prevent corrosion processes

when different materials have to be combined

Sealing: The use of adhesives lead to a reduction of secondary

sealing processes

Load transfer: Reduced notch sensitivity (FRP!) due to uniform,

plane load transfer through the adhesive layer.

Styling: High potential of variation in styling due to the possibility to

combining different materials.


Automotive/Railway and Aerospace Industries

General conditions for Structural Adhesive Bonding

Aerospace Railway Automotive (cars)

Adhesive storage Ideal controlled storage conditions (shelf life)

Ambient conditions for

storage

Ambient conditions for

storage

Surface treatment Careful, expensive surface preparation

Minimal, manual surface

preparation

No or fast automated

surface preparation

processes

Small volume production Small/medium volume

production

High volume production

Manufacturing Very high degrees of manual operation

High degree of manual

operation

Complete automated

fabrication

Autoclave cure cycle Room temperature curing Fast curing cycles (e.g. heat,

electromagnetic)

Durability Complex, expansive procedures of bonded parts

during life time > 20 year

Minimal inspection during life

time of 30 years

No inspection during life time

of 10-30 years

Recycling Recycling concepts have to be available


Automotive/Railway and Aerospace Industries Shear strength Vs Strain (Various Adhesive Types)


Automotive/Railway and Aerospace Industries Shear strength Vs Bond Line Thickness

5

10

15

20

25

30

35

40

1 2 3 4 5

She

ar S

tren

gth,

[M

Pa]

Bond Line Thickness, [mm]

Aerospace

Formula 1

Hang-ons

Windscreen


Automotive/Railway and Aerospace Industries Examples of Structural Adhesive Bonding for Composites

Aircrafts Race Cars Trucks Cars

Concept Cars Buses Sport Cars Helicopters

A380

Fiber Metal Laminate McLaren – Formula 1

CFRP Thermoset

Car Body Structure

SMC Thermoset Parts

for Driver Cabin

GMT-Thermoplastic

Rotor Blade

Erosion Protection CFRP Thermoset

Car Body Structure

SMC Thermoset

Panels

Injection Moulded

Thermoplastic Car Body



Mercedes CL-Coupe


New Boing 747

Automotive/Railway and Aerospace Industries CFRP

AFRP

CFRP

CFRP

GFRP


JAS Gripen – Swedish Military Aircraft


Bonding

Bonding


Automotive/Railway and Aerospace Industries Adhesives are also used in the boat and railway industry


Introduction

Dental


Industries - Medicine

Injury Breakout


Need to:


• To join the components of medical devices

• Bone repair – filling space – joining prosthesis to bone

• Wound sealing, wound closure


Laceration to lower

eyebrow

Closed wound with

adhesive.

Three months after

treatment with adhesive

Cyanoacrylate tissue

adhesives combine

cyanoacetate and

formaldehyde in a heat

vacuum along with a

base to form a liquid

monomer. When the

monomer comes into

contact with moisture on

the skin's surface, it

chemically changes into

a polymer that binds to

the top epithelial layer.




../../../../../../



And of course for everyday use

FRP strengthening for flexure Structural Bonding in the Building Industry


Building Industry General motivation for adhesive structural bonding

Lightweight construction: Adhesives improve the stiffness and

strengths of bonds. Therefore the weight of structures and car-bodies

can be reduced.

Mixed Materials: Realization of structural bonding concepts of

different substrates (FRP, metals, glasses, ceramics etc.)

Crash performance: Improvements are possible by the use of

substrates and adhesives with a high potential of energy absorption

Long time performance: Adhesives prevent corrosion processes

when different materials have to be combined

Sealing: The use of adhesives lead to a reduction of secondary

sealing processes

Load transfer: Reduced notch sensitivity (FRP!) due to uniform,

plane load transfer through the adhesive layer.

Styling: High potential of variation in styling due to the possibility to

combining different materials.


Building Industry General motivation for adhesive structural bonding

• New Built (Bridges, flooring, matched moulding technique)

• Repair and strengthening (Plate Bonding, patch repairs etc.)

• FRP Structures (Composite action, joints, etc.)


Building Industry

New Built


History – Plate Bonding 1964

1975- 1988 1990- 1993- 2002

Tomorrow ? Steel Plates,

•South Africa

Steel Plates

• Sweden FRP

• Japan

FRP

• Switzerland • Canada • USA

FRP

• UK • Sweden • Denmark • etc.

Steel Plates

• France • UK • Japan • Switzerland • USA

• Development of strong epoxy adhesives • Development of FRP materials • Demand for repair and strengthening methods


Future Bonding Possibilities

We need adhesives that:

• are durable over time/during loading

• can transfer high forces

• are environmental friendly

• can be applied on/in wet surfaces/areas

• can be applied at low temperatures

• harden fast

• bond against a majority of materials

• can be recycled

• are cost effective



Does such an adhesive exist?

• To some extent it does – but these “adhesives”

may not be applicable to all type of applications.

• The adhesives need to be more tailor-made

• We have to be more careful when designing for

structural applications



Better grip (bond) when driving?

Learn from nature??


Future Bonding Possibilities Bonding under water to a variety of materials?

Mussel “adhesive” bonding to Teflon

Acorn Barnacle “adhesive”

bonding to stone

the importance of bonding an historic overview and future possibilities · 2016. 4. 14. · general...

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