Adhesive Bonding 2024/2025 PDF

ADVANCED MATERIALS AND JOINING Adhesive Bonding Course 2024/2025  Introduction Theory of adhesion Surface treatment Adhesive selection Control (destructive and non-destructive tests) 2  INTRODUCTION Advanced mate...

ADVANCED MATERIALS AND JOINING Adhesive Bonding Course 2024/2025  Introduction Theory of adhesion Surface treatment Adhesive selection Control (destructive and non-destructive tests) 2  INTRODUCTION Advanced materials  Composite Materials Joining technologies Mechanical joints Welding ADHESIVES 3  INTRODUCTION: APPLICATIONS Aeronautical industry 4  INTRODUCTION: APPLICATIONS Automotive industry Lotus Elise 5  INTRODUCTION: APPLICATIONS Rail industry Hexcel composites 6  INTRODUCTION: APPLICATIONS Marine industry Sika 7  INTRODUCTION: APPLICATIONS Bridge over River Fulda (Kassel, Germany) Civil industry Ultra high performance concrete (UHPC)-steel Deck plates are glued to the upper chords of the truss structure The Helix Bridge (London, UK) Glass and steel retractable footbridge The glass is bonded to the transoms with structural- grade adhesive Fehling, 2013 8  INTRODUCTION: APPLICATIONS Electrical industry Shoe industry 9 INTRODUCTION: ADVANTAGES AND LIMITATIONS ADVANTAGES Uniform stress distribution Ability to joint dissimilar materials and thin-sheet materials Increase in design flexibility (e.g. honeycomb structures) Smooth surfaces Continuous contact between surfaces In general, reduce costs LIMITATIONS Peeling and cleavage Limited resistance to extreme conditions (heat, temperature…) Need of fixing tools during curing: economic disadvantage Surface treatment Adhesives are frequently cured at high temperature Difficult quality control: development of non-destructive testing 10  THEORY OF ADHESION Why do adhesives stick? 11  THEORY OF ADHESION Theories of adhesion Physical Chemical Mechanical adsorption adsorption interlocking - Surface forces - Chemical bond - High surface area -Most important - Requires good - Occurs in all wettability bonds 12  THEORY OF ADHESION Forces involved All the bonds are forces acting in very short distances (some angstroms (1 A = 10-10 m = 0.0001 mm)). Secondary bonds Primary bonds 13  THEORY OF ADHESION Surface roughness ≈ 0.5 μm 14  THEORY OF ADHESION Surface roughness Roughness = 1000 x distance of action of the bonding forces But if liquid… 15  THEORY OF ADHESION Wetting 16  THEORY OF ADHESION Wetting Liquid/Solid Unbalance of attraction forces at the surface of solids/liquids  surface energy/surface tension 17  THEORY OF ADHESION Wetting 18  THEORY OF ADHESION Wetting: spreading Principle of minimum energy Surfaces with high energy Surfaces with low energy Hard materials Soft materials High melting point Low melting point Metals, ceramics Organic solids, polymers 19  THEORY OF ADHESION Wetting: spreading 20  THEORY OF ADHESION Wetting: spreading Same solid Same liquid 21  THEORY OF ADHESION How can joints be improved? SURFACE TREATMENTS 22  SURFACE TREATMENTS Characteristics that affect adhesion Contamination: oils, greases, fingerprints, mold release agents, etc. have low surface energy  Decrease adhesion Weak boundary layer: contaminant films, oxide layers, rust, corrosion, scale, and loose surface particles, etc. 23  SURFACE TREATMENTS In surface treatment, the following operations can occur: 1- Material removal 2- Chemical modification of the surface 3- Change of the surface topography Good treatment Bad treatment 24  SURFACE TREATMENTS Classification Passive processes No chemical alteration Clean the surface Remove substances that are weakly attached Active processes Chemical transformation Metals  formation of a well-defined oxide or structure Polymers  formation of polar groups that increase surface energy and adhesion Last treatment when high strength and durability are required 25  SURFACE TREATMENTS Classification Pasive treatments Active treatments Solvents Acid etching Chemical cleaning Primers Abrasive methods: sanding, Anodizing (metals) shot-blasting Flame treatment, plasma (polymers) 26  SURFACE TREATMENTS Tests Surface energy Roughness 27 28  ADHESIVE SELECTION Classification Function Mechanical Hardening Physical form performance mechanism Structural Liquid Non-structural Rigid Chemical reaction Paste Elastic Loss of solvent or Solid water Hardening from the melt 29  ADHESIVE SELECTION Classification by function Structural Non-structural Epoxies Silicones Polyurethanes Cyanoacrylates Acrylics Hot melts 30  ADHESIVE SELECTION Classification by mechanical performance Rigid/Stiff Elastic Epoxies Silicones Acrylics Polyurethanes Cyanoacrylates Hot melts 31  ADHESIVE SELECTION Classification by hardening mechanism Chemical reaction Loss of solvent of water Hardening from the melt Two parts Contact adhesives Thermoplastics Cure by humidity White glue Hot melts Cure by radiation (light, UV…) Catalized by the substrate 32  ADHESIVE SELECTION Epoxies Polyurethanes Silicones One or two parts Cure by moisture Cure by moisture Strong but brittle Elastic structural adhesive Elastic and high water resistance Aircrafts, sport equipment Automotive industry Molds, household appliances Acrylics Acrylics – Anaerobics Acrylics – Cyanoacrylates One or two parts Cure by absence of oxygen and Cure by substrates moisture Lower strength than epoxies triggered by metallic ions Rigid with bad gap filling Rapid assemble of structures Threadlockers Optical and electronics Pressure-sensitive adhesive Cure by pressure Rapid assembly Medicine, labelling 33  ADHESIVE SELECTION Selection process Substrate Product requirements Adhesive selection Experimental validation Design and loading Service environment 34  CONTROL: DESTRUCTIVE TESTING Loading modes It is important to consider the environment where the adhesive joint is going to be during its in- service life. Polymers are sensitive to chemicals, temperature, moisture and radiation. 35  CONTROL: DESTRUCTIVE TESTING Shear: single lap joints 𝐹𝐹 (𝑁𝑁) 𝜎𝜎(𝑀𝑀𝑀𝑀𝑀𝑀) = 𝐴𝐴( 𝑚𝑚𝑚𝑚2 ) 36  CONTROL: DESTRUCTIVE TESTING Tension: pull-off tests 𝐹𝐹 (𝑁𝑁) 𝜎𝜎(𝑀𝑀𝑀𝑀𝑀𝑀) = 𝐴𝐴( 𝑚𝑚𝑚𝑚2 ) 37  CONTROL: DESTRUCTIVE TESTING Peel and cleavage 𝐹𝐹 (𝑁𝑁) 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 (𝑁𝑁/𝑚𝑚𝑚𝑚) = 𝑙𝑙(𝑚𝑚𝑚𝑚) 38  CONTROL: DESTRUCTIVE TESTING Creep and Fatigue - Static loads are applied gradually and remain constant over time. - Cyclic loads involve repetitive or fluctuating forces that can cause stress and fatigue in materials. - Creep refers to the slow, time-dependent deformation of a material under a constant load. All types of loads are critical considerations in the selection and performance of adhesives, as they determine the durability and longevity of the bonded joints under different operating conditions. 39  CONTROL: NON-DESTRUCTIVE TESTING Visual inspection Porosity, misalignments, non-uniform adhesive thickness, etc. Da Silva, 2011 40  CONTROL: NON-DESTRUCTIVE TESTING Tap test Tapping on the bonded joint Sharp clear tone  good adhesion Dull hollow tone  void or unattached area Can be instrumented (solenoid operated hammer and microphone pickup) 41  CONTROL: NON-DESTRUCTIVE TESTING Ultrasonic inspection There are a transmitter and a receiver of ultrasounds, which can be in one or two probes. 42  CONTROL: NON-DESTRUCTIVE TESTING Laser ultrasonic inspection Ultrasounds are generated and detected by laser. 43  CONTROL: NON-DESTRUCTIVE TESTING Acoustic emission Joint must be loaded (semi-destructive) Stress waves emitted by crack propagation or micro-cracking are recorded with piezoelectric transducers The only method that can detect poor adhesion An, 2014 44  CONTROL: NON-DESTRUCTIVE TESTING Radiography Voids or discontinuities Contrast improved with metal powder or other suitable filler 45  CONTROL: NON-DESTRUCTIVE TESTING Thermal methods: Infrared thermography Ruwandi Fernando, 2019 46