Editorial

5 pages, 228 KiB

Open AccessEditorial

by Raul D. S. G. Campilho

Processes 2023, 11(12), 3369; https://doi.org/10.3390/pr11123369 - 04 Dec 2023

Cited by 2 | Viewed by 1011

Adhesive bonded joints have become vital to modern engineering, offering advantages such as weight reduction, enhanced fatigue performance, and improved stress distribution [...] Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

Research

Jump to: Editorial, Review

19 pages, 5537 KiB

Open AccessArticle

Static and Fatigue Characterization of Adhesive T-Joints Involving Different Adherends

by Georgino C. G. Serra, José A. M. Ferreira and Paulo N. B. Reis

Processes 2023, 11(9), 2640; https://doi.org/10.3390/pr11092640 - 04 Sep 2023

Cited by 1 | Viewed by 741

Abstract

It is very important to understand the damage mechanisms as well as the mechanical response of T-joints involving different materials on the base plate. For this purpose, two configurations were studied. In one, the joint is composed of a base plate and a [...] Read more.

It is very important to understand the damage mechanisms as well as the mechanical response of T-joints involving different materials on the base plate. For this purpose, two configurations were studied. In one, the joint is composed of a base plate and a T-element, both in Al 6063-T5, while in the other one, the aluminum base plate was replaced by a glass fiber composite. Finally, each configuration was divided into two batches, where in one, the elements were bonded with a stiff adhesive (Araldite^® AV 4076-1/HY 4076) while in the other, a more ductile adhesive (Araldite^® AW 106/HV 953 U) was used. The static and fatigue strength of all configurations was evaluated in bending. In all cases, the damage occurred at the end of the T-element, where a crack appeared and propagated toward the interior of the T-joint. The bending strength is highest for joints involving aluminum and the ductile adhesive, which is 2.8 times higher than the same configuration involving composite base plates and 1.7 times higher than that using the stiff adhesive. Finally, the highest fatigue lives were obtained for T-joints involving Al 6063-T5 base plates, and regardless of the base plate material, the ductile adhesive promoted the highest fatigue strength. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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12 pages, 4611 KiB

Open AccessArticle

Analysis of Hydrothermal Ageing on Mechanical Performances of Fibre Metal Laminates

by Costanzo Bellini, Vittorio Di Cocco, Francesco Iacoviello, Larisa Patricia Mocanu, Gianluca Parodo, Luca Sorrentino and Sandro Turchetta

Processes 2023, 11(8), 2413; https://doi.org/10.3390/pr11082413 - 10 Aug 2023

Viewed by 609

Abstract

Fibre Metal Laminates (FMLs) are very interesting materials due to their light weight coupled with their high stiffness, high fatigue resistance, and high damage tolerance. However, the presence of the polymeric matrix in the composite layers and of polymeric adhesive at the metal/composite [...] Read more.

Fibre Metal Laminates (FMLs) are very interesting materials due to their light weight coupled with their high stiffness, high fatigue resistance, and high damage tolerance. However, the presence of the polymeric matrix in the composite layers and of polymeric adhesive at the metal/composite interface can constitute an Achille’s heel for this class of materials, especially when exposed to a hot environment or water. Therefore, in the present article, aluminium/carbon fibre FML specimens were produced, aged by considering different hydrothermal conditions, and then, subjected to mechanical testing. The End-Notched Flexure (ENF) test was considered for this activity. It was found that the first ageing stage, consisting of submersion in saltwater, was very detrimental to the specimens, while the second stage, composed of high and low temperature cycles, showed an increase in the maximum load, probably due to a post-curing effect of the resin during the higher temperatures of the ageing cycles and to the dissolution of salt crystals during the subsequently ageing stages in distilled water. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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24 pages, 14470 KiB

Open AccessArticle

Coupled Excitation Strategy for Crack Initiation at the Adhesive Interface of Large-Sized Ultra-Thin Chips

by Tao Wu, Xin Chen, Shiju Wen, Fangsong Liu and Shengping Li

Processes 2023, 11(6), 1637; https://doi.org/10.3390/pr11061637 - 26 May 2023

Cited by 1 | Viewed by 889

Abstract

The initial excitation of interface crack of large-size ultra-thin chips is one of the most complicated technical challenges. To address this issue, the reversible fracture characteristics of a silicon-based chip (chip size: 1.025 mm × 0.4 mm × 0.15 mm) adhesive layer interface [...] Read more.

The initial excitation of interface crack of large-size ultra-thin chips is one of the most complicated technical challenges. To address this issue, the reversible fracture characteristics of a silicon-based chip (chip size: 1.025 mm × 0.4 mm × 0.15 mm) adhesive layer interface was examined by scanning electron microscope (SEM) tests, and the characteristics of a cohesive zone model (CZM) unit were obtained through peel testing. The fitting curve of the elastic bilinear model was in high agreement with the experimental data, with a correlation coefficient of 0.98. The maximum energy release rate required for stripping was G_C = 10.3567 N/m. Subsequently, a cohesive mechanical model of large-size ultra-thin chip peeling was established, and the mechanical characteristics of crack initial excitation were analyzed. The findings revealed that the larger deflection peeling angle in the peeling process resulted in a smaller peeling force and energy release rate (ERR), which made the initial crack formation difficult. To mitigate this, a coupling control method of structure and force surface was proposed. In this method, through structural coupling, the change in chip deflection was greatly reduced through the surface coupling force, and the peeling angle was greatly improved. It changed the local stiffness of the laminated structure, made the action point of fracture force migrate from the center of the chip to near the edge of the chip, the peeling angle was increased, and the energy release rate was locally improved. Finally, combined with mechanical analysis and numerical simulation of the peeling process, the mechanical characteristics of peeling were analyzed in detail. The results indicated that during the initial crack germination process, the ERR of the peel interface is significantly increased, the maximum stress value borne by the chip is significantly reduced, and the peel safety and reliability are greatly improved. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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16 pages, 6498 KiB

Open AccessArticle

Evaluation of XD 10 Polyamide Electrospun Nanofibers to Improve Mode I Fracture Toughness for Epoxy Adhesive Film Bonded Joints

by Stefania Minosi, Fabrizio Moroni and Alessandro Pirondi

Processes 2023, 11(5), 1395; https://doi.org/10.3390/pr11051395 - 04 May 2023

Viewed by 1323

Abstract

The demand for ever-lighter structures raises the interest in bonding as a joining method, especially for materials that are difficult to join with traditional welding and bolting techniques. Structural adhesives, however, are susceptible to defects, but can be toughened in several ways: by [...] Read more.

The demand for ever-lighter structures raises the interest in bonding as a joining method, especially for materials that are difficult to join with traditional welding and bolting techniques. Structural adhesives, however, are susceptible to defects, but can be toughened in several ways: by changing their chemical composition or by adding fillers, even of nanometric size. Nanomaterials have a high surface area and limited structural defects, which can enhance the mechanical properties of adhesives depending on their nature, quantity, size, and interfacial adhesion. This work analyzes the Mode I fracture toughness of joints bonded with METLBOND^® 1515-4M epoxy film and XantuLayr electrospun XD 10 polyamide nanofibers. Two joint configurations were studied, which differed according to the position of the nanomat within the adhesive layer: one had the nanofibers at the substrate/adhesive interfaces, and the other had the nanofibers in the center of the adhesive layer. Double cantilever beam joints were manufactured to evaluate the Mode I fracture toughness of the bonding with and without nano-reinforcement. The nanofibers applied at the substrate/adhesive interface improved the Mode-I fracture toughness by 32%, reaching the value of 0.55 N/mm. SEM images confirm the positive contribution of the nanofibers, which appear stretched and pulled out from the matrix. No fracture toughness variation was detected in the joints with the nanofibers placed in the middle of the adhesive layer. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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11 pages, 1688 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Removable Pressure-Sensitive Adhesives Based on Acrylic Telomer Syrups

by Mateusz Weisbrodt and Agnieszka Kowalczyk

Processes 2023, 11(3), 885; https://doi.org/10.3390/pr11030885 - 15 Mar 2023

Viewed by 1541

Abstract

Removable pressure-sensitive adhesives (PSAs) are used in the production of self-adhesive materials such as protective films, masking tapes or biomedical electrodes. This work presents a new and environmentally friendly method of obtaining this type of adhesive materials, i.e., photochemically induced free radical telomerization. [...] Read more.

Removable pressure-sensitive adhesives (PSAs) are used in the production of self-adhesive materials such as protective films, masking tapes or biomedical electrodes. This work presents a new and environmentally friendly method of obtaining this type of adhesive materials, i.e., photochemically induced free radical telomerization. Adhesive binders to removable PSAs, i.e., the photoreactive acrylic telomer syrups (ATS) were prepared from n-butyl acrylate, acrylic acid, and 4-acrylooxybenzophenone. Tetrabromomethane (CBr₄) or bromotrichloromethane (CBrCl₃) were used as the telogens. ATS was modified with unsaturated polybutadiene resin and a radical photoinitiator. Adhesive compositions were coated onto a carrier and UV cross-linked. The effects of the chemical nature of telomers (i.e., terminal Br or Cl atoms) and their molecular weight (K-value), as well as the cross-linking degree on adhesive properties of PSAs, were studied. It was found that with the increase in telogen content in the system, the dynamic viscosity of ATS and K-value of acrylic telomers decrease, and the conversion of monomers increases. CBr₄ turned out to be a more effective chain transfer agent than CBrCl₃. Moreover, telomers with terminal Br-atoms (7.5 mmol of CBr₄), due to slightly lower molecular weights and viscosity, showed a higher photocrosslinking ability (which was confirmed by high cohesion results at 20 and 70 °C, i.e., >72 h). Generally, higher values of the temperature at which adhesive failure occurred were noted for PSAs based on ATS with lower telogen content (7.5 mmol), both CBr₄ and CBrCl₃. The excellent result for removable PSA was obtained in the case of telomer syrup Br-7.5 crosslinked with a 5 J/cm² dose of UV-radiation (adhesion ca.1.3 N/25 mm, and cohesion > 72 h). Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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15 pages, 21762 KiB

Open AccessArticle

A Laser Shock-Based Disassembly Process for Adhesively Bonded Ti/CFRP Parts

by Panagiotis Kormpos, Selen Unaldi, Laurent Berthe and Konstantinos Tserpes

Processes 2023, 11(2), 506; https://doi.org/10.3390/pr11020506 - 07 Feb 2023

Cited by 4 | Viewed by 1434

Abstract

The application of adhesively bonded joints in aerospace structural parts has increased significantly in recent years and the general advantages of their use are well-documented. One of the disadvantages of adhesive bonding is the relevant permanence, when compared to traditional mechanical fastening. End-of-life [...] Read more.

The application of adhesively bonded joints in aerospace structural parts has increased significantly in recent years and the general advantages of their use are well-documented. One of the disadvantages of adhesive bonding is the relevant permanence, when compared to traditional mechanical fastening. End-of-life processes generally require the separation of the adherents for repair or recycling, and usually to achieve this, they combine large mechanical forces with a high temperature, thus damaging the adherents, while consuming large amounts of energy. In this work, a novel disassembly technique based on laser-induced shock waves is proposed for the disassembly of multi-material adhesively bonded structures. The laser shock technique can generate high tensile stresses that are able to break a joint, while being localized enough to avoid damaging the involved adherents. The process is applied to specimens made from a 3D-woven CFRP core bonded to a thin Ti layer, which is a common assembly used in state-of-the-art aircraft fan blades. The experimental process has been progressively developed. First, a single-sided shot is applied, while the particle velocity is measured at the back face of the material. This method proves ineffective for damage creation and led to a symmetric laser configuration, so that the tensile stress can be controlled and focused on the bond line. The symmetric approach is proved capable of generating a debonding between the Ti and the CFRP and propagating it by moving the laser spot. Qualitative assessment of the damage that is created during the symmetric experimental process indicates that the laser shock technique can be used as a material separation method. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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13 pages, 3022 KiB

Open AccessArticle

Determination of the Bonding Strength of Finger Joints Using a New Test Specimen Geometry

by Hannes Stolze, Michael Gurnik, Sebastian Kegel, Susanne Bollmus and Holger Militz

Processes 2023, 11(2), 445; https://doi.org/10.3390/pr11020445 - 02 Feb 2023

Cited by 1 | Viewed by 2040

Abstract

In this study, a specimen geometry for testing finger joints was developed using finite element simulation and proofed by experimental testing. Six different wood species and three adhesives were used for finger-jointing specimens. With the test specimen geometry, the bonding strength of the [...] Read more.

In this study, a specimen geometry for testing finger joints was developed using finite element simulation and proofed by experimental testing. Six different wood species and three adhesives were used for finger-jointing specimens. With the test specimen geometry, the bonding strength of the finger joints was determined without the usual self-locking of the joint. Under load, the test specimen geometry introduces maximum stress at the beginning of the bond line (adhesive zone). However, the test specimen geometry does not generate a symmetric stress state. The main difficulty here is the flank angle of the finger joint geometry. The wood species and adhesives significantly influenced the performance of the finger joints. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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16 pages, 7175 KiB

Open AccessEditor’s ChoiceArticle

Adhesive Thickness and Ageing Effects on the Mechanical Behaviour of Similar and Dissimilar Single Lap Joints Used in the Automotive Industry

by Raffaele Ciardiello, Carlo Boursier Niutta and Luca Goglio

Processes 2023, 11(2), 433; https://doi.org/10.3390/pr11020433 - 01 Feb 2023

Cited by 4 | Viewed by 1454

Abstract

The effects of the adhesive thickness and overlap of a polyurethane adhesive have been studied by using different substrate configurations. Single lap joint (SLJ) specimens have been tested with homologous substrates, carbon fibre-reinforced plastics and painted metal substrates. Furthermore, a configuration with dissimilar [...] Read more.

The effects of the adhesive thickness and overlap of a polyurethane adhesive have been studied by using different substrate configurations. Single lap joint (SLJ) specimens have been tested with homologous substrates, carbon fibre-reinforced plastics and painted metal substrates. Furthermore, a configuration with dissimilar substrates has been included in the experimental campaign. Both types of these adhesive and substrates are used in the automotive industry. The bonding procedure has been carried out without a surface treatment in order to quantify the shear strength and stiffness when surface treatments are not used on the substrates, reproducing typical mass production conditions. Three different ageing cycles have been used to evaluate the effects on SLJ specimens. A finite element model that uses cohesive modelling has been built and optimised to assess the differences between the different adopted SLJ configurations. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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11 pages, 8685 KiB

Open AccessArticle

The Effect of Organic Fillers on the Mechanical Strength of the Joint in the Adhesive Bonding

by Nergizhan Anaç and Zekeriya Doğan

Processes 2023, 11(2), 406; https://doi.org/10.3390/pr11020406 - 30 Jan 2023

Cited by 3 | Viewed by 1860

Abstract

The most important advantages of adding additives to adhesives are increasing the bonding strength and reducing the adhesive cost. The desire to reduce costs as well as the need for environmentally friendly and health-friendly products have paved the way for the recycling of [...] Read more.

The most important advantages of adding additives to adhesives are increasing the bonding strength and reducing the adhesive cost. The desire to reduce costs as well as the need for environmentally friendly and health-friendly products have paved the way for the recycling of waste materials and the use of cheaper natural materials as additives. In this study, mussel, olive pomace, and walnut powders in different ratios (5%, 15%, and 30% by weight) and in different sizes (38 and 45 µm) were added to an epoxy adhesive. The steel materials were joined in the form of single-lap joints by using the obtained adhesives with additives. These joints were subjected to the tensile test and the strengths of these joints were examined. SEM images of the bonding interface were taken, and the distribution of the powders was examined. When the powder size was 45 µm, bond strengths increased in all additive ratios compared to the pure adhesive, while for 38 µm powders, the strength value increased only at the 5% additive ratio. In joints with 45 µm powder additives, the strength increased by up to 38% compared to the pure adhesive, while this rate was determined as 31% for 38 µm. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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17 pages, 3492 KiB

Open AccessFeature PaperArticle

Reuse of Carbon Fibers and a Mechanically Recycled CFRP as Rod-like Fillers for New Composites: Optimization and Process Development

by José Antonio Butenegro, Mohsen Bahrami, Miguel Ángel Martínez and Juana Abenojar

Processes 2023, 11(2), 366; https://doi.org/10.3390/pr11020366 - 24 Jan 2023

Cited by 2 | Viewed by 2383

Abstract

The rising amount of carbon fiber reinforced polymer (CFRP) composite waste requires new processes for reintroducing waste into the production cycle. In the present research, the objective is the design and study of a reuse process for carbon fibers and CFRP by mechanical [...] Read more.

The rising amount of carbon fiber reinforced polymer (CFRP) composite waste requires new processes for reintroducing waste into the production cycle. In the present research, the objective is the design and study of a reuse process for carbon fibers and CFRP by mechanical recycling consisting of length and width reduction, obtaining rods and reintegrating them as fillers into a polymeric matrix. Preliminary studies are carried out with continuous and discontinuous unidirectional fibers of various lengths. The processing conditions are then optimized, including the length of the reinforcement, the need for a plasma surface treatment and/or for resin post-curing. The resin is thermally characterized by differential scanning calorimetry (DSC), while the composites are mechanically characterized by tensile strength tests, completed by a factorial design. In addition, the composites tested are observed by scanning electron microscopy (SEM) to study the fracture mechanics. Optimal processing conditions have been found to reduce the reinforcement length to 40 mm while maintaining the mechanical properties of continuous reinforcement. Furthermore, the post-curing of the epoxy resin used as matrix is required, but a low-pressure plasma treatment (LPPT) is not recommended on the reinforcement. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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23 pages, 13030 KiB

Open AccessArticle

Influence of Loading Rate on the Cohesive Traction for Soft, Rubber-Like Adhesive Layers Loaded in Modes I and III

by Peer Schrader, Dennis Domladovac and Stephan Marzi

Processes 2023, 11(2), 356; https://doi.org/10.3390/pr11020356 - 22 Jan 2023

Cited by 2 | Viewed by 1087

Abstract

To date, the fracture behaviour of soft, polyurethane-based adhesive joints has rarely been investigated. This work contributes to the experimental investigation of such joints in modes I and III by performing double cantilever beam (mode I) and out-of-plane loaded double cantilever beam (mode [...] Read more.

To date, the fracture behaviour of soft, polyurethane-based adhesive joints has rarely been investigated. This work contributes to the experimental investigation of such joints in modes I and III by performing double cantilever beam (mode I) and out-of-plane loaded double cantilever beam (mode III) tests at various loading rates. The tests were evaluated using a J-integral method, which is well established for testing stiff adhesive layers and is conventionally used to determine the cohesive traction at the crack tip. Additionally, fibre-optics measurements were conducted to provide crack extension, process zone length, and cohesive traction from the measured backface strain of the adherends. It was found that the energy release rate seems to be largely independent of the loading mode. However, differences were observed regarding process zone length and resistance curve behaviour. Furthermore, the backface strain measurement allows the determination of the cohesive traction along with the complete adhesive layer as well as separation and separation rate, yielding rate-dependent cohesive laws. A comparison indicated that the cohesive traction obtained from the J-integral method does not match the measured benchmark from the backface strain measurements because the underlying theoretical assumptions of the J-integral method are likely violated for soft, rubber-like adhesive joints. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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19 pages, 5439 KiB

Open AccessArticle

Numerical Modelling and Validation of Mixed-Mode Fracture Tests to Adhesive Joints Using J-Integral Concepts

by Luís F. R. Neves, Raul D. S. G. Campilho, Isidro J. Sánchez-Arce, Kouder Madani and Chander Prakash

Processes 2022, 10(12), 2730; https://doi.org/10.3390/pr10122730 - 17 Dec 2022

Cited by 3 | Viewed by 1440

Abstract

The interest in the design and numerical modelling of adhesively-bonded components and structures for industrial application is increasing as a research topic. Although research on joint failure under pure mode is widespread, applied bonded joints are often subjected to a mixed mode loading [...] Read more.

The interest in the design and numerical modelling of adhesively-bonded components and structures for industrial application is increasing as a research topic. Although research on joint failure under pure mode is widespread, applied bonded joints are often subjected to a mixed mode loading at the crack tip, which is more complex than the pure mode and affects joint strength. Failure of these joints under loading is the objective of predictions through mathematical and numerical models, the latter based on the Finite Element Method (FEM), using Cohesive Zone Modelling (CZM). The Single leg bending (bending) testing is among those employed to study mixed mode loading. This work aims to validate the application of FEM-CZM to SLB joints. Thus, the geometries used for experimental testing were reproduced numerically and experimentally obtained properties were employed in these models. Upon the validation of the numerical technique, a parametric study involving the cohesive laws’ parameters is performed, identifying the parameters with the most influence on the joint behaviour. As a result, it was possible to numerically model SLB tests of adhesive joints and estimate the mixed-mode behaviour of different adhesives, which enables mixed-mode modelling and design of adhesive structures. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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Review

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18 pages, 23523 KiB

Open AccessReview

Design and Experimental Analysis of an Adhesive Joint for a Hybrid Automotive Wheel

by Jens-David Wacker, Tobias Kloska, Hannah Linne, Julia Decker, Andre Janes, Oliver Huxdorf and Sven Bose

Processes 2023, 11(3), 819; https://doi.org/10.3390/pr11030819 - 09 Mar 2023

Cited by 2 | Viewed by 1893

Abstract

When it comes to lightweight design of automotive wheels, hybrid designs consisting of a carbon composite wheel rim and a metallic, e.g., aluminum alloy, wheel disc offer significant potential. However, the conventionally used bolted joint between the two parts is complex and requires [...] Read more.

When it comes to lightweight design of automotive wheels, hybrid designs consisting of a carbon composite wheel rim and a metallic, e.g., aluminum alloy, wheel disc offer significant potential. However, the conventionally used bolted joint between the two parts is complex and requires compromises in lightweight design due to the additional mechanical elements. Within this research, an adhesive joint for a hybrid wheel is developed in order to demonstrate its performance and lightweight potential. The main challenges are the reliable resistance against high structural loads during different load cases, as well as the residual stresses in the joint due to different thermal expansion rates of the composite and aluminum material. The developed joint combines an adhesive bond with a form-fitted geometry while still enabling an assembling process of the wheel disc in rotational direction. In addition, adaptations of the fiber layup in the rim area significantly reduce the thermal residual stresses in the joint by 47%. Subcomponent specimens, which represent the joint of an aluminum spoke with the composite rim, are manufactured and tested at different temperatures and load cases. The test results show sufficient strength of the adhesive joint as well as an improvement of the developed form-fitted joint compared to a basic adhesive bond. The adhesively joined wheel offers a lightweight potential of 6% compared to the bolted wheel. Full article

(This article belongs to the Special Issue Design of Adhesive Bonded Joints)

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