Adhesive Bonding Technology and Testing E-Book

Ricardo Joao Camilo Carbas

• Herausgeber: Wiley-VCH GmbH
• Kategorie: Fachliteratur
• Sprache: Englisch
• Veröffentlichungsjahr: 2023

Seitenzahl: 242

Beschreibung

Provides insights purpose and design of experiments for adhesive bonding, considering adhesive bond testing as well as joint design and strength prediction.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Preface

1 Simple Practical Demonstrations

1.1 Importance of Loading Mode on Bonded Joint Performance

1.2 Surface Treatments and Methods to Evaluate Surface Energy

1.3 Stress Distribution Along the Overlap Length

1.4 Visual Identification of Defects in Adhesive Joints

1.5 Failure Analysis of Adhesive Joints

2 Production and Testing

2.1 Bulk Specimens

2.2 Thick Adherend Shear Specimens

2.3 Fracture Mechanics Specimens

2.4 Single‐Lap Joint Specimens

3 Laboratorial Activities and Report Examples

3.1 Effect of Surface Treatment on the Mechanical Behavior of Adhesively Bonded Joints

3.2 Effect of Adhesive Type and Overlap Length on the Failure Load of Adhesively Bonded Joints

3.3 Effect of Adhesive Thickness on the Failure Load of Adhesively Bonded Joints

3.4 Effect of Overlap Length on the Strength and Failure Mechanism of Composite Adhesive Joints

3.5 Modeling a Single‐Lap Joint Using Finite Element Analysis and Cohesive Zone Modeling

3.6 Case Study in Joint Design for a Structural Automotive Application

References

4 Essay and Multi‐choice Questions

4.1 Essay Questions

4.2 Multi‐choice Questions

Solutions

Essay Questions – Example Answers

Multi‐choice Questions – Solutions

Index

End User License Agreement

List of Tables

Chapter 3

Table 3.1 High‐density polyethylene (HDPE) properties.

Table 3.2 Adherend dimensions (HDPE).

Table 3.3 Adhesive properties.

Table 3.4 Mechanical properties of the polymeric adherend and of the adhesiv...

Table 3.5 Contact angles after three distinct surface treatments.

Table 3.6 High‐strength steel properties (DIN 55 Si 7 treated).

Table 3.7 Adhesive properties.

Table 3.8 Mechanical properties of the high‐strength steel adherend.

Table 3.9 Mechanical properties of the applied adhesives.

Table 3.10 Failure load of the different samples.

Table 3.11 Failure loads obtained through different analytical criteria and ...

Table 3.12 Properties of treated DIN St33 steel.

Table 3.13 Properties of the adhesive BETAMATETM 2098.

Table 3.14 Predictions of joint failure forces according to the generalized ...

Table 3.15 Experimental results for adhesive bonds of 0.2 mm and 1 mm thickn...

Table 3.16 Properties of the glass fiber composite.

Table 3.17 Adhesive properties of SikaForce®‐7818 L7.

Table 3.18 Dimensions of the tested specimens.

Table 3.19 Mechanical properties of fiberglass composite.

Table 3.20 Mechanical properties of SikaForce®‐7818 L7 adhesive.

Table 3.21 Failure load predicted by the Goland and Reissner model for diffe...

Table 3.22 Failure load prediction by the generalized yield criterion for di...

Table 3.23 Relative error of the breaking force predicted by the different m...

Table 3.24 Properties of the high‐strength steel.

Table 3.25 Properties of brittle adhesive.

Table 3.26 Example of cohesive properties for a brittle epoxy adhesive.

Table 3.27 Key mechanical properties of the XNR6862‐E3 adhesive.

Table 3.28 Key joint design parameters.

Table 3.29 Comparison of predicted failure load values.

Table 3.30 Comparison between the predicted design loads and the experimenta...

List of Illustrations

Chapter 1

Figure 1.1 Schematic representation of the shear and cleavage loads acting o...

Figure 1.2 Adhesive joint under pull‐out force.

Figure 1.3 Adhesive joint subjected to shear stress, with the area being ove...

Figure 1.4 Adhesive joint subjected to shear stress, with the area being ove...

Figure 1.5 Adhesive joint using adhesive tape and aluminum adherends, subjec...

Figure 1.6 Experimental testing procedure of an adhesive joint using adhesiv...

Figure 1.7 Schematic representation of the shear and peel behavior of an adh...

Figure 1.8 Angle of contact (θ) formed between an adherend surface and ...

Figure 1.9 Variation of the contact angle of a drop of liquid as a function ...

Figure 1.10 Wetting of a surface with a liquid before and after surface trea...

Figure 1.11 Manual cleaning of a surface using acetone and a cloth.

Figure 1.12 Observation of the shape of a drop of water with a liquid of kno...

Figure 1.13 Use of Dyne pens on a metallic surface before (a) and after (b) ...

Figure 1.14 Surface of the polymeric material to be treated with plasma.

Figure 1.15 Observation of the shape of a drop of water with a liquid of kno...

Figure 1.16 Dyne pen application on a polymeric non‐treated (a) and plasma‐t...

Figure 1.17 Schematic representation of adhesive joints subjected to shear a...

Figure 1.18 Typical bonded joint geometries for a joint under shear stress....

Figure 1.19 Schematic representation of the vertical trace along the length ...

Figure 1.20 Single lap joint in an unloaded state.

Figure 1.21 Single lap joint in a loaded state.

Figure 1.22 Schematic representation of stress concentration in an adhesive ...

Figure 1.23 Types of defects that can be found in an adhesive joint.

Figure 1.24 Good and bad practice in adhesive application.

Figure 1.25 Good and bad practice in top adherend application.

Figure 1.26 Adhesive joint with geometric misalignment of one of the adheren...

Figure 1.27 Adhesive joint showing areas of burnt adhesive due to excessive ...

Figure 1.28 Adhesive joint missing adhesive in parts of the overlap area.

Figure 1.29 Detection of voids with the aid of a coin by the analysis of the...

Figure 1.30 Schematic representation of the different failure modes in singl...

Figure 1.31 Adhesive joint with adhesive failure.

Figure 1.32 Adhesive joint with cohesive failure in the adhesive.

Figure 1.33 Adhesive joint with adherend failure.

Figure 1.34 Cohesive failure in the adhesive layer, in metallic adhesive joi...

Figure 1.35 Mixed failure (cohesive and adhesive failure).

Figure 1.36 Example of delamination failure of composite joints.

Chapter 2

Figure 2.1 Tensile specimens produced with injecting techniques.

Figure 2.2 Tensile specimens produced with adhesive pouring techniques.

Figure 2.3 Schematic representation of pouring technique.

Figure 2.4 Technical drawing of a metallic mold used in the pouring techniqu...

Figure 2.5 Removal ofdust and particles from the mold surface.

Figure 2.6 Application of mold release agent.

Figure 2.7 Assembly of different parts of the mold and positioning of the si...

Figure 2.8 Equipment used to ensure proper mixing of adhesives supplied in s...

Figure 2.9 Two different techniques to apply the adhesive: (a) with the use ...

Figure 2.10 Mold closure process.

Figure 2.11 Application of pressure on the closed mold.

Figure 2.12 After curing procedure, the mold is opened (a), unfasted (b), th...

Figure 2.13 Tensile test geometry (dimensions in mm).

Figure 2.14 Tensile specimens after machined.

Figure 2.15 Mechanical tests of tensile tests using extensometer (a) and vid...

Figure 2.16 Two methods to manufacture TAST specimens: (a) machined adherend...

Figure 2.17 Metallic mold used to manufacture TAST specimens.

Figure 2.18 Application of the release agent.

Figure 2.19 Sandblasting the area where adhesive will be applied.

Figure 2.20 Anodized adherend surface.

Figure 2.21 Laboratorial setup used to anodize adherends (a) and surface to ...

Figure 2.22 Schematic representation of the position of shims to control the...

Figure 2.23 Positioning of the shims and the adherends in the mold.

Figure 2.24 Application of the adhesive using a nozzle (a) or a spatula (b)....

Figure 2.25 Closing of the mold (a) and closing the mold (b).

Figure 2.26 Removing the shims (a) and the excess of adhesive from the joint...

Figure 2.27 Setup used to test the TAST specimens according to the ISO 11003...

Figure 2.28 Assembly of transducers in TAST specimens.

Figure 2.29 Two methods to obtain DCBs: (a) cutting out specimens and (b) bo...

Figure 2.30 Different techniques to apply loads: (a) drilled holes, (b) bond...

Figure 2.31 Mold usedto manufacture the specimens.

Figure 2.32 Removal of dirt and dust from the mold.

Figure 2.33 Application of release agent in the mold.

Figure 2.34 Technique used to create a pre‐crack in the bonded area, (a) sch...

Figure 2.35 Positioning of adherends and spacers in the mold.

Figure 2.36 Adhesive application using a spatula (a) and a nozzle (b).

Figure 2.37 Placement of upper adherend using a rotational movement.

Figure 2.38 Removal of excess adhesive using a coarse file.

Figure 2.39 Schematic representation of DCB test (a) and ENF test (b) loadin...

Figure 2.40 Setup used to measure the real crack propagation during the DCB ...

Figure 2.41 Geometry of SLJs according to ASTM D 1002 (dimensions in mm).

Figure 2.42 Different surface treatments: (a) sandblasting, (b) anodizing, a...

Figure 2.43 Construction scheme of SLJs using shims to control the parameter...

Figure 2.44 Different techniques to control the adhesive thickness (a) with ...

Figure 2.45 Application of the adhesive using a spatula (a) and with a nozzl...

Figure 2.46 Positioning of upper adherend after applying the adhesive using ...

Figure 2.47 Removal of excess adhesive from the joint.

Figure 2.48 The misalignment of SLJ during the test.

Figure 2.49 SLJ testing setup using bonded tabs (a) or tightened tabs, both ...

Figure 2.50 Rotation during testing that introduces bending moments at the e...

Chapter 3

Figure 3.1 Example of surfaces with lower wetting (a) and good wetting (b)....

Figure 3.2 Shear stress on a single‐lap joint: most basic analysis.

Figure 3.3 Different types of wetting, spread (a) and poor wet (b).

Figure 3.4 Contact angles between the ethylene and PE surface untreated (ace...

Figure 3.5 Contact angles between the ethylene and PE surface treated with a...

Figure 3.6 Testing pens with untreated bonding area.

Figure 3.7 Testing pens with plasma‐treated bonding area.

Figure 3.8 Load–displacement curves of plasma treated and cleaned joints.

Figure 3.9 A typical load–displacement curve of the joints with surfaces tre...

Figure 3.10 Fracture of the untreated bonded area.

Figure 3.11 Mechanical behavior of the plasma‐treated bonded area.

Figure 3.12 Volkersen analysis, joint unload (a), joint loaded (b), and shea...

Figure 3.13 Single‐overlap joint as analyzed by Volkersen (1938).

Figure 3.14 Joint strength prediction method based on the adhesive and adher...

Figure 3.15 Stress distribution along the overlap for brittle and flexible a...

Figure 3.16 Schematic representation of a single‐lap joint.

Figure 3.17 Tensile tests of the single‐overlap joints.

Figure 3.18 Failure types on adhesive bonding – cohesive (a) and adhesive (b...

Figure 3.19 Fracture surface of the SikaForce 7817 L7's joint with 25 mm of ...

Figure 3.20 Fracture surface of the SikaForce 7817 L7's joint with 50 mm of ...

Figure 3.21 Fracture surface of the AV138/HV998's joint with 25 mm of overla...

Figure 3.22 Fracture surface of the AV138/HV998's joint with 50 mm of overla...

Figure 3.23 Failure load for joints with ductile adhesives according to diff...

Figure 3.24 Failure load for joints with brittle adhesives according to diff...

Figure 3.25 Schematic explanation of the plastic shear on the adhesive.

Figure 3.26 Comparison of experimental and predicted failure load.

Figure 3.27 Failure surface (a) and adherend yielding (b) of adhesive joints...

Figure 3.28 Failure surface (a) and adherend yielding (b) of adhesive joints...

Figure 3.29 Interlaminar failure of composite adherends.

Figure 3.30 Failure of the composite in adhesive joints.

Figure 3.31. Single‐overlap joint (b – adherend width; ta – adherend thickne...

Figure 3.32 Load–displacement curve for 12.5 mm overlap length.

Figure 3.33 Load–displacement curve for 25 mm overlap length.

Figure 3.34 Joint with an overlap length of 12.5 mm, after failure.

Figure 3.35 Joint with an overlap length of 25 mm, after failure.

Figure 3.36 Failure load as a function of overlap length.

Figure 3.37 Failure load as a function of overlap length.

Figure 3.38 Distribution of peel stress in the adhesive joint determined by ...

Figure 3.39 Peel stress along the overlap length (l = 12.5 mm).

Figure 3.40 Peel stress along the overlap length (l = 25 mm).

Figure 3.41 Predicted and experimental failure load as a function of overlap...

Figure 3.42 Example of a single‐lap joint being modeled in Abaqus.

Figure 3.43 Suggested unit system for modeling of adhesively bonded joints....

Figure 3.44 Possible modeling approaches in Abaqus.

Figure 3.45 Use of multiple cohesive element layers in a single‐lap joint, w...

Figure 3.46 Triangular cohesive law for two loading modes (a) and examples o...

Figure 3.47 Summary of experimental testing methodologies used for determini...

Figure 3.48 Workflow through the different Abaqus modules.

Figure 3.49 Design and extrusion of a single‐lap joint shape (left) and the ...

Figure 3.50 Process for importing a sketch created in an external software....

Figure 3.51 Process for importing a model created in an external software....

Figure 3.52 Example of a simplified model geometry, using symmetry to analyz...

Figure 3.53 Key properties used for modeling of adhesives.

Figure 3.54 Setting elastic properties for cohesive modeling in the Edit Mat...

Figure 3.55 Setting stress limits for cohesive modeling in the Edit Material...

Figure 3.56 Defining damage evolution parameters in the Suboption Editor wit...

Figure 3.57 Section Assignment Manager showing correlation between Sections,...

Figure 3.58 Creation of Sections and assigning them to previously defined ma...

Figure 3.59 Defining the section assigned to a specific model region.

Figure 3.60 Create Step menu, showing some of the many model steps permitted...

Figure 3.61 Edit Step menu, showing the incrementation control.

Figure 3.62 Example of boundary conditions suitable for modeling a single‐la...

Figure 3.63 Create Load and Create Boundary Condition menus, listing the typ...

Figure 3.64 Main meshing tools available in Abaqus.

Figure 3.65 Mesh Control menu.

Figure 3.66 Correct redefinition of a Sweep Path, showing the arrow (red) pe...

Figure 3.67 Field Output Request tools.

Figure 3.68 Process of creation of two sets of nodes, one for extracting dis...

Figure 3.69 History Output Requests Manager, showing the possibility to requ...

Figure 3.70 Field Output Requests Manager, showing the possibility to reques...

Figure 3.71 Job Manager menu, showing the Write Input, Data Check, Submit, M...

Figure 3.72 Visualization of stiffness degradation within the adhesive layer...

Figure 3.73 Example of a load–displacement curve generated using history out...

Figure 3.74 Process for saving the reaction forces as a XY dataset.

Figure 3.75 Process for saving the spatial displacement as a XY dataset.

Figure 3.76 Combining the displacement and load using the Operate on XY data...

Figure 3.77 Joint design workflow.

Figure 3.78 A vehicle sill side beam joint.

Figure 3.79 The configuration of the bonded area under analysis.

Figure 3.80 Relative advantages and disadvantages of adhesives in automotive...

Figure 3.81 Dimensions of the bonded area under consideration.

Figure 3.82 Main families of structural adhesives used in the automotive ind...

Figure 3.83 Relative performance of four different adhesives used in the aut...

Figure 3.84 Comparison between the tensile curves for a crash‐resistant adhe...

Figure 3.85 Stress–strain curve for the 6063 T6 aluminum alloy under conside...

Figure 3.86 Image of an anodization process (right) and the end result (left...

Figure 3.87 Key mechanical testing procedures used for the characterization ...

Figure 3.88 Tensile stress–strain curve (left) and shear stress–strain curve...

Figure 3.89 Adhesive creep curves obtained at different temperatures being u...

Figure 3.90 Main design parameters under consideration.

Figure 3.91 Joint design approaches.

Figure 3.92 Analytical models used for strength prediction in this work.

Figure 3.93 Relative advantages and disadvantages of the strength of materia...

Figure 3.94 General construction of the model.

Figure 3.95 Boundary conditions of the model.

Figure 3.96 Mesh of the model.

Figure 3.97 Deformed model shape.

Figure 3.98 Evolution of the stiffness degradation damage parameter (SDEG) w...

Figure 3.99 Three‐point bending setup used for testing the T‐joint under ana...

Figure 3.100 Three‐point bending setup used for testing the T‐joint under an...

Figure 3.101 Failure mode of the tested joint.

Figure 3.102 Comparison between the experimental load–displacement curves of...

Figure 3.103 Fracture surface of the alternative joint bonded with Henkel 50...

Figure 3.104 Key design points in the design for manufacturing of bonded joi...

Figure 3.105 Fixture used to simultaneously produce two T‐joints, showing th...

Figure 3.106 Curing of the T‐joint specimens in a specialized hot plate pres...

Figure 3.107 Curing cycle of the T‐joint specimens in a specialized hot plat...

Guide

Cover

Table of Contents

Title Page

Copyright

Preface

Begin Reading

Solutions

Index

End User License Agreement

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Adhesive Bonding Technology and Testing

Ricardo João Camilo Carbas

Eduardo André Sousa Marques

Alireza Akhavan‐Safar

Ana Sofia Queirós Ferreira Barbosa

Lucas Filipe Martins da Silva

Authors

Dr. Ricardo João Camilo CarbasINEGI ‐ Inst. of Science and Innovationin Mechanical EngineeringDept. of Mechanical EngineeringRua Dr. Roberto Frias s/n4200‐465 PortoPortugal

Dr. Eduardo André Sousa MarquesINEGI ‐ Inst. of Science and Innovationin Mechanical EngineeringRua Dr. Roberto Frias 4004200‐465 PortoPortugal

Dr. Alireza Akhavan‐SafarINEGI ‐ Inst. of Science and Innovationin Mechanical EngineeringRua Dr. Roberto Frias 4004200‐465 PortoPortugal

Dr. Ana Sofia Queirós Ferreira BarbosaINEGI ‐ Inst. of Science and Innovationin Mechanical EngineeringRua Dr. Roberto Frias 4004200‐465 PortoPortugal

Prof. Lucas Filipe Martins da SilvaUniversity of PortoDept. of Mechanical EngineeringRua Dr. Roberto Frias s/n4200‐465 PortoPortugal

Cover Image: © Jenson/Shutterstock

All books published by WILEY‐VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

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© 2023 WILEY‐VCH GmbH, Boschstraße 12, 69469 Weinheim, Germany

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Print ISBN: 978‐3‐527‐35051‐3

ePDF ISBN: 978‐3‐527‐83800‐4

ePub ISBN: 978‐3‐527‐83801‐1

oBook ISBN: 978‐3‐527‐83802‐8

Preface

This book is intended to serve as a didactic tool to support both those teaching and learning the subject of adhesive bonding. While the companion book “Introduction to Adhesive Bonding” is mostly dedicated to the theoretical aspects of this joining technology, this book is more concise and highly focused on hands‐on learning, with exercises and their solutions and multiple experimental activities.

The book is divided into four parts. The first is dedicated to simple practical demonstrations of adhesive bonding. These are all simple activities suitable to be carried out in a classroom setting, which quickly highlight the advantages and limitations of this technique. The second part is dedicated to production and testing of specimens that are used to characterize adhesives and the most commonly used types of joints. The third part describes in detail multiple laboratorial activities suitable for implementation in the laboratorial classes of engineering courses. These activities explore aspects such as the manufacture of defect‐free bonded joints, the effects of geometry and materials properties in adhesive joint testing, surface preparation and joint design and strength prediction, among many others. Lastly, a set of exercises is provided in the form of developmental questions and multiple choice questions. This last part focuses on all of the knowledge areas discussed in the companion “Introduction to Adhesive Bonding” book. All problems are provided with solutions, and many are fully solved, helping bachelor or masters students in their study and providing evaluation reference materials for teachers.

The authors would like to thank Paulo Nunes for the help in the preparation of figures.

They also want to thank the team of WILEY, especially Felix Bloeck, for the excellent cooperation during the preparation of this book.

Porto, Portugal, 2022 Ricardo João Camilo Carbas   

Eduardo André Sousa Marques  

Alireza Akhavan‐Safar       

Ana Sofia Queirós Ferreira Barbosa

Lucas Filipe Martins da Silva   

1Simple Practical Demonstrations

1.1 Importance of Loading Mode on Bonded Joint Performance

1.1.1 Introduction

Adhesive bonding shows many advantages over more traditional methods of joining such as bolting, brazing, and welding or even the use of mechanical fasteners. No other joining technique is so versatile, and its transversality lies in its capacity to join different materials, its ability to ensure permanent assembly, and its ease of use. In fact, a well‐designed bonded joint allows for a reduction in production costs, while maintaining proper mechanical properties of the joint.

Adhesives work by exploring the adhesion phenomena, and they are usually polymeric materials, typically thermosetting, that, compared to materials that are joined in structural applications (such as metals and composites), show a much lower strength. Nonetheless, adhesive joints can be applied to a wide diversity of structures, withstanding different types of loads. To understand the mechanics of a bonded joint, it is important to first establish that the behavior of the joint is highly dependent on the type of loads it is sustaining. In an attempt to obtain the highest joint strength, it is fundamental to load the adhesive under forces acting in the plane of the adhesive layer, minimizing peeling loads. Joints are generally more resistant when shear‐stressed because the adhesive layer is relatively well aligned with the loading direction. In these conditions, the entirety of the adhesive layer can positively contribute to sustain the load (see Figure 1.1). Joints subjected to cleavage or peel stresses are much weaker than those subjected to shear because the stresses are concentrated in a very small area. All the stress is located at the edge of the joint (see Figure 1.1).

1.1.2 Equipment

One set of scissors

Tensile testing machine

Figure 1.1 Schematic representation of the shear and cleavage loads acting on adhesive joints.

1.1.3 Materials

One roll of double‐sided foam adhesive tape

Small aluminum beams

1.1.4 Safety Precautions

Apply the necessary safety procedures for operating a test machine.

1.1.5 Experimental Procedure

1.1.5.1 In Class

Peel the adhesive tape off the roll by applying a pulling force or “peeling” action as shown in Figure 1.2. See how easily it peels away, even if the adhesive is quite strong.

Figure 1.2 Adhesive joint under pull‐out force.

Figure 1.3 Adhesive joint subjected to shear stress, with the area being overlapped with and without the adhesive.

Now, cut two strips of adhesive tape, approximately 10 cm long. Bond the two strips parallel to each other with an overlap of approximately 3 cm. Bond the glued side of one strip to the unglued side of the other strip (see Figure 1.3). Pull on the joint in order to try to separate the strips by loading them parallelly to the adhesive layer, thereby subjecting the adhesive to shear, as schematically represented in Figure 1.3. It will be much harder to separate the joint as we are now loading it in shear; however, because of the low stiffness of the tape, it will bend and introduce some peeling loads, as shown in Figure 1.3, and this peeling can promote debonding.

Repeat the same procedure, but this time, join the strips so that the sides that have adhesive are in direct contact, as represented in Figure 1.4. When the joint is made between the glued side of both strips, it is impossible to separate the strips under shear. Ultimately, the strips will break, while the bonded area remains intact.

1.1.5.2 In the Laboratory

In order to better understand the influence of load type when an adhesive joint is used, the same tape will be bonded to an aluminum plate, and the response for two different types of load (shear and peel) will be studied using a universal tensile machine.

Figure 1.4 Adhesive joint subjected to shear stress, with the area being overlapped with the adhesive on both strips.

To this aim, the same tape will now be applied to metal (aluminum) adherends. Cut an adhesive tape strip, approximately 10 cm long, and join it to the surface of an aluminum adherend with a 3 cm overlap. This adhesive joint is subjected to shear stress, as shown in Figure 1.5. As the adherend is much stiffer, this adhesive joint is now subjected to an almost uniform shear stress.

The procedure will now be replicated, but this time, the forces exerted will be in a peeling direction. Therefore, it is recommended for the tape strip to be slightly longer so that it can be easily pulled off. Cut an adhesive tape strip, approximately 15 cm long, and join it to the surface of an aluminum adherend with 3 cm of overlap. This adhesive joint can now be subjected to peeling stress, as shown in Figure 1.6.

A comparison of the loads applied on the manufactured joints can be done manually or using a testing machine. Manually, it is possible to “feel” that the forces are different, but they cannot be quantified. Therefore, using a universal testing machine, the behavior of the joints loading under different types of stresses and different surface states can be easily quantified, leading to different results. Figure 1.7 shows a schematic representation of the peel and shear forces. As “felt” in a manual test, when an adhesive joint is tested in peel stress, at first, it is necessary to exert a greater force to peel off the adhesive, but over the course of the test, the force required decreases and the joint eventually fails. In turn, when the adhesive joint is being tested at shear, the force required gradually increases until failure occurs.

Figure 1.5 Adhesive joint using adhesive tape and aluminum adherends, subjected to shear stresses.

Figure 1.6