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 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. 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. 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 Making of and adhesive, Ancient Egypt 1930 A.D: Epoxies
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)
Introduction 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 Adhesive Organic Non-Organic Natural Animal Vegetable Mineral Natural Rubber etc. Synthetic Cements Silicates Ceramic Epoxy Polyurethane Phenol Polyester Vinyl ester Acrylics Melt adhesives.
Introduction 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 surfacefree energy value of the substrate the liquid molecules stay bound together Poor wetting means a poor bond!
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 Bad Wetting Introduction Good Wetting This is important to achieving a good bond
Adhesive Joints Introduction 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
Modes of Failure A uniform stress pattern in an adhesive joint is seldom produced by the application of external force. Structural failure Introduction Adhesion failure Cohesive failure
Introduction Loads on Adhesive Bonded Joints Tension Compression Shear Cleavage Both parts are rigid Peel 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
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 Surface treatment Manufacturing Durability Recycling Ideal controlled storage conditions (shelf life) Careful, expensive surface preparation Small volume production Very high degrees of manual operation Ambient conditions for storage Minimal, manual surface preparation Small/medium volume production High degree of manual operation Ambient conditions for storage No or fast automated surface preparation processes High volume production Complete automated fabrication Autoclave cure cycle Room temperature curing Fast curing cycles (e.g. heat, electromagnetic) 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 concepts have to be available
Automotive/Railway and Aerospace Industries Shear strength Vs Strain (Various Adhesive Types)
Shear Strength, [MPa] FRP strengthening for flexure 40 35 Automotive/Railway and Aerospace Industries Shear strength Vs Bond Line Thickness Aerospace 30 25 20 15 Formula 1 10 5 Hang-ons Windscreen 1 2 3 4 5 Bond Line Thickness, [mm]
Automotive/Railway and Aerospace Industries Examples of Structural Adhesive Bonding for Composites Aircrafts Race Cars Trucks Cars A380 Fiber Metal Laminate McLaren Formula 1 CFRP Thermoset Car Body Structure SMC Thermoset Parts for Driver Cabin GMT-Thermoplastic Helicopters Sport Cars Buses Concept Cars Rotor Blade Erosion Protection CFRP Thermoset Car Body Structure SMC Thermoset Panels Injection Moulded Thermoplastic Car Body
Automotive/Railway and Aerospace Industries Mercedes CL-Coupe
Automotive/Railway and Aerospace Industries New Boing 747 CFRP CFRP GFRP AFRP CFRP
Automotive/Railway and Aerospace Industries 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
Industries - Medicine Need to: To join the components of medical devices Bone repair filling space joining prosthesis to bone Wound sealing, wound closure
Industries - Medicine 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.
Industries - Medicine
Automotive/Railway and Aerospace Industries And of course for everyday use
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
1964 Steel Plates, South Africa History Plate Bonding Tomorrow? 1975-1988 1990-1993- 2002 Steel Plates France UK Japan Switzerland USA Steel Plates Sweden FRP Japan FRP Switzerland Canada USA FRP UK Sweden Denmark etc. Development of strong epoxy adhesives Development of FRP materials Demand for repair and strengthening methods
We need adhesives that: Future Bonding Possibilities 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
Future Bonding Possibilities 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
Future Bonding Possibilities 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