Thickness Of Adhesive Layer Research Articles

Adaptive phase-field modeling of fracture in orthotropic composites

An adaptive phase-field method is developed and applied to model fracture propagation in orthotropic composites. The proposed approach extends the work of Muixí et al. (2020) to orthotropic composites through following modifications: (a) elastic tensor is evaluated in the global coordinate system from a given engineering stiffness matrix in the principal material coordinates, (b) strain energy density is additively decomposed into fiber and matrix-dominated modes, and (c) a penalized second-order structural tensor is introduced in the phase-field equation facilitating preferential damage growth along the fiber orientation. The developed approach is validated through several benchmark examples and available experimental results.Several numerical failure experiments are conducted varying fiber orientation, adhesive layer thickness, shear modulus, and fracture toughness. A large increase in ductility and peak-load carrying capacity is observed for laminate configurations where the fibers are oriented such that the principal material coordinates and the global coordinates are aligned. An increase in the adhesive layer’s fracture toughness increases the macroscopic ductility and prevents catastrophic failure of laminate. The results of this study provide valuable insights into the failure mechanisms in orthotropic composites.

Effect of Modified Triple-Layer Application on the Bond Strength of Different Dental Adhesive Systems to Dentin.

The goal of this article was to assess the effect of modified triple-layer application (MTLA) in conjunction with the active bonding technique on the bond strength of four adhesive systems to dentinal substrate. The adhesives tested were Prime&Bond Universal (PBU), OptiBond Universal (OBU), OptiBond FL (OBFL), and Clearfil SE (CSE). The adhesives were applied according to the following strategies: single active application (A) and triple adhesive layer application including Active-Passive-Passive (APP); AAP; and AAA. The micro-tensile bond strength test was evaluated following 24 h or 6 months of storage. The composite-dentin interface morphology was investigated using scanning electron microscopy. The data were statistically analyzed with a significance level of α = 0.05. At 24 h of aging, all of the factors tested were not significant (p > 0.05) for CSE. For OBFL, OBU, and PBU, statistically higher values were observed for the A technique (p < 0.05). Plus, there were no significant variances between the APP, AAP, and AAA techniques (p > 0.05) for OBFL and PBU. However, for OBU, there were no significant differences between the A and AAA techniques (p > 0.05). After 6 months of aging, the A technique showed statistically higher values when compared to the other techniques (p < 0.01), except for OBFL, where the A and AAA techniques showed promising outcomes. When comparing the bond strength values of 24 h and 6 months, only for PBU, all of the techniques used resulted in bond strength stability over time (p > 0.05). Thicker adhesive layers were observed when MTLA was applied. Only the OBFL adhesive showed the formation of resin tags in all of the modalities tested. The bonding performances of the different application techniques used were material-dependent.

Metal-Metal Bonding Process Research Based on Xgboost Machine Learning Algorithm.

Conventionally, the optimization of bonding process parameters requires multi-parameter repetitive experiments, the processing of data, and the characterization of complex relationships between process parameters, and performance must be achieved with the help of new technologies. This work focused on improving metal-metal bonding performance by applying SLJ experiments, finite element models (FEMs), and the Xgboost machine learning (ML) algorithm. The importance ranking of process parameters on tensile-shear strength (TSS) was evaluated with the interpretation toolkit SHAP (Shapley additive explanations) and it optimized reasonable bonding process parameters. The validity of the FEM was verified using SLJ experiments. The Xgboost models with 70 runs can achieve better prediction results. According to the degree of influence, the process parameters affecting the TSS ranked from high to low are roughness, adhesive layer thickness, and lap length, and the corresponding optimized values were 0.89 μm, 0.1 mm, and 27 mm, respectively. The experimentally measured TSS values increased by 14% from the optimized process parameters via the Xgboost model. ML methods provide a more accurate and intuitive understanding of process parameters on TSS.

Dynamic analysis of adhesive layer on active vibration control

This paper investigates the influence of the adhesive layer between the piezoelectric actuator and the base structure on the structural bending response in active vibration control. The adhesive layer plays a crucial role in transmitting longitudinal vibrations between layers. However, its influence on structural bending response remains unclear. Two dynamic coupling models were developed for a partially covered beam using Hamilton’s principle, with different considerations for shear deformation in the adhesive layer. Validation through finite element analysis shows the dynamic model accounting for shear deformation has wider applicability across adhesive types. Overlooking the adhesive layer leads to overestimating actuator performance. Vibration control sensitivity to adhesive Young’s modulus underscores its significance. Optimizing actuation efficiency involves adjusting adhesive layer thickness based on its modulus. The contribution of this study is to provide guidance for piezoelectric actuators installation and adhesive selection for effective active control system design.

Long‐term performance of single‐lap joints: Review, challenges and prospects in civil engineering

AbstractCompared with traditional technology, bonding technology is more suitable for civil structure reinforcement because of its cost‐efficiency and superior mechanical properties. However, research on the long‐term performance of single‐lap joints (SLJs) requires better organization and comprehension. This article aims to investigate the long‐term performance and optimization design of SLJs. The main factors influencing the long‐term performance of SLJs from both material and component levels are discussed. The moisture diffusion mechanisms of bulk adhesives and the degradation mechanisms of SLJs are explored. Moreover, the optimization design of SLJs focuses on evaluating the overlap length, adhesive layer thicknesses, and changes in adhesives along the overlap length based on available literature. It is found that the applicability of diffusion models should be validated, and the selection of the models should consider working environments and types of adhesives. Exploring failure mechanisms and design criteria for the mixed SLJs in hygrothermal environments with/without sustained or alternating load is significant for the optimization design. This article indicates the limitations on the shear strength and long‐term performance of SLJs in available studies and provides insights into the challenges and prospects of their optimization design.

On adhesively bonded joints with a mixed failure mode—An experimental and numerical study

Cohesive zone model (CZM) has been extensively used to study interfacial failure behaviors such as fracture of adhesively bonded joints (ABJs). Accurate and efficient identification of traction–separation law (TSL) in CZM signifies an important issue for design and analysis of adhesive structures. In this study, a modified Arcan fixture was developed and employed to investigate the mixed mode failure behaviors of ABJs for carbon fiber reinforced plastic (CFRP) substrates under a tensile-shear coupling load, in which the double cantilever beam (DCB) test was carried out to characterize fracture toughness for benchmark data. With the help of digital image correlation (DIC) technique, the interfacial displacement field was obtained. The virtual crack closure technique (VCCT) was adopted to decouple the mode mixture at different tension-shear angles of the Arcan specimens. Based on the traction–separation law for each mixed ratio of failure mode, a refined CZM was established. In this study, the Arcan and DCB specimens bonded with a flexible adhesive of 3M DP190 were prepared and tested. The experiments were carried out for the ABJs with two adhesive layer thicknesses of 0.3 mm and 1 mm, respectively, to investigate the influence of bonding thickness. Based on the extracted CZM parameters, a finite element (FE) analysis model was developed and validated with the experimental results. Unlike the traditional predetermined damage evolution law, a new CZM was established without a priori cohesive damage evolution; and the effectiveness of the proposed model for the TSL extraction was verified. By using this method, the mechanical response of the bonding interface under complex stress state was well predicted and the FE modeling of ABJ’s fracture was accurately achieved. The study is anticipated to gain new understanding and fundamental data on mixed failure mode, thereby enabling better design of ABJs for engineering applications.

A study of the particle-reinforced bonded joint performance

In this study, a systematic study has been performed to explore the influence of the adhesive particle fillers on the mechanical performance of bonded joints. Three-dimensional finite element models were established to analyse the strength of bonded joints. Based on response surface methodology, experiments were designed with three parameters and three levels. Experimental results were applied to develop response surface models between parameters (adhesive layer thickness, particle size, and particle volume fraction) and response values (shear strength and peel strength). Response surface models incorporating genetic algorithms were applied to find the optimal set of input parameters. These findings indicated that the interaction between volume fraction and adhesive layer thickness has the most significant influence on the shear strength of joints, and the interaction between particle size and adhesive layer thickness has a major effect on the peel strength of joints. The optimal set of process parameters is: adhesive layer thickness 0.54 mm, particle size 69 µm, and volume fraction 4.0%.

Investigation of the suitability of adhesive tapes for sealing building structures of various surfaces

Adhesive sealing tapes play an important role in ensuring the air tightness of the building, affecting the indoor microclimate and efficient energy use. However, there is still a lack of objective indicators that would demonstrate the ability of the sealing tape to ensure the long-term air tightness of the sealing joints of various building structures. Therefore, the purpose of this work is to investigate the indicators demonstrating the suitability of adhesive sealing tapes for sealing building structures of different surfaces and deformation, to provide detailed analyses of the results, and to propose practical recommendations. The investigated self-adhesive tapes differed in backing (nonwoven material, plastic reinforced film, paper, metal foil) and adhesives (acrylic and butyl). The materials of the sealed structural joints were plywood, OSB, plasterboard, cement sawdust board, plastered board, and plastic. The thickness, deformability, peel and shear adhesion of the self-adhesive tapes were used to determine its suitability for sealing of different structural joints. It was determined that tapes with higher deformability are more versatile, as they are suitable for sealing joints subjected to small and large deformations. The higher peel adhesion is typical for tapes of an air-permeable non-woven material backing and a thin adhesive layer. Tapes with a thicker adhesive layer are most suitable for sealing complex-shaped joints. Tapes with acrylic adhesive have a higher peeling force from smooth and moderately smooth surfaces, whereas butyl adhesive creates better contact with uneven surfaces in highly deformable joints.

Vibration and damping of carbon fiber reinforced polymer orthogonal lattice truss sandwich panels manufactured by a new manufacturing process

A new method of fabricating carbon fiber reinforced polymer (CFRP) orthogonal lattice truss sandwich panels is proposed. Inner trusses are inserted into outer trusses. Three structures are prepared using different adhesives: epoxy resin, ethylene–vinyl acetate copolymer (EVA), and nitrile butadiene rubber (NBR). The mode shapes, natural frequencies, and loss factors of the structures are tested and predicted using the finite element modal strain energy method with a solid model and two shell models, respectively. The shell stiffness matrixes are calculated using representative volume element (RVE) method and analytical method. The results show that these three theories can accurately predict the sandwich panels with epoxy or EVA adhesive, while the sandwich panel with rubber layer cannot be accurately predicted. The strain energy composition, shell stiffness matrices, influence of node offset and influence of adhesive layer thicknesses are studied. The EVA adhesive improves the loss factors of the structure within an acceptable reduction of natural frequency.

Reliability analysis of composite laminate patch repaired structures based on response surface proxy model

In this paper, the reliability analysis of composite laminate patch repaired structures under unidirectional static load was studied by means of a probability model. First, a proxy model for the maximum static load carrying capacity of the repaired structure was established using quadratic polynomial response surface method (RSM) considering the repair material properties, repair patch design and adhesive layer thickness. Second, the probability distribution input of various basic random parameters including geometric characteristics and material properties were considered based on actual repair data. Finally, both the reliability and sensitivity analysis of the repaired structure were investigated by means of Monte Carlo simulation method. The results show that the reliability analysis model is of great significance for the subsequent design and properties evaluation of composite repaired structures.

Influence of adhesive thickness and defect on mechanical property of adhesive bonded joint of flexible polymer substrate and cable for solar panel application

Flexible polymer substrate and flat polymer cable were adhesive bonded to fabricate the solar panel in the present study. The relationship between the adhesive thickness, mechanical properties and fracture morphologies of the joints were systematically investigated to figure out how the adhesive layers with different thickness affected the joints’ mechanical properties. The influence of the defects on the joint quality was also studied via an artificial defect introduction method. Adhesive failure accompanied with low tensile-shear strength was easy to occur to the joints with extremely thin adhesive thickness due to the weak boundary formation between the adhesive and the adherent. When the adhesive thickness increased, the joints started to show the cohesive failure with higher tensile-shear strength since the adhesive completely fill the surface crevices. The joints’ mechanical properties however decreased again with further increasing the adhesive thickness, owing to the generation of more defects and higher residual stress within the thicker adhesive layer. On the other hand, adhesive failure was more likely to occur around the defect, which significantly deteriorated the joints’ mechanical properties. The defect located in the center of the bonding area led to a larger adhesive fractured area, thereby having a greater impact on the mechanical properties in comparison to the same-size defect located in the corner or the marginal center.

Simultaneous nondestructive estimation of thickness and longitudinal wave velocity of adhesive layers in adhesive joints through air-coupled ultrasonic testing

This paper proposes a nondestructive method for the simultaneous estimation of the thickness and longitudinal wave velocity of an adhesive layer using a transmission coefficient spectrum, including amplitude and phase spectra measured via air-coupled ultrasonic testing to confirm adhesive joint reliability. The method correctly estimated the values of the adhesive layer from the transmission coefficient spectrum experimentally, unlike the conventional estimation using only the amplitude spectra. The absolute values of the estimation errors of thickness and longitudinal wave velocity obtained using this method were 1.3–12.1% and 0.4–6.1%, respectively. The proposed method can be useful for the quality assurance of adhesive joints.

Printability of (Quasi-)Solid Polysiloxane Electrolytes for Online Dye-Sensitized Solar Cell Fabrication

Dye-sensitized solar cells (DSSCs) are a very promising solution as remote sustainable low power sources for portable electronics and Internet of Things (IoT) applications due to their room-temperature and low-cost fabrication, as well as their high efficiency under artificial light. In addition, new achievements in developing semitransparent devices are driving interest in their implementation in the building sector. However, the main obstacle towards the large-scale exploitation of DSSCs mainly concerns their limited long-term stability triggered by the use of liquid electrolytes. Moreover, the device processing generally involves using a thick adhesive separator layer and vacuum filling or injection of the liquid polymer electrolyte between the two electrodes, a method that is difficult to scale up. This review summarizes the advances made in the design of alternative (quasi-)solid polymer electrolytes, with a focus on polysiloxane-based poly(ionic liquid)s. Their behavior in full DSSCs is presented and compared in terms of power generation maximization, advantages and shortcomings of the different device assembly strategies, as well as polymer electrolyte-related processing limitations. Finally, a fair part of the manuscript is allocated to the assessment of liquid and gel polymer electrolyte printability, particularly focusing on polysiloxane-based electrolytes. Spray, blade (slot-dye), screen and inkjet printing technologies are envisaged considering the polymer electrolyte thermophysical and rheological properties, as well as DSSC processing and operating conditions.

Water uptake on lightning strike damage of carbon fiber reinforced composites with surface protections

The effect was examined of water uptake on the lightning strike (LS) damage of carbon fiber reinforced composites (CFRCs) and surface-protected CFRCs. First, water absorption (WA) experiments on CFRC, CFRC adhered to a copper mesh (CFRC-Cu) and CFRC bonded with an aluminum coating (CFRC-Al) were performed to obtain specimens with various water contents. Then, simulated LS tests were carried out on the specimens to investigate the LS damage mechanism. The experimental results showed that the LS damage level of the pristine CFRC specimens increased with the addition of water content, primarily due to the decreased glass transition temperature of the matrix, the increased longitudinal electrical conductivity and the gas explosion after WA. In terms of the CFRC-Cu specimens, the decreased interfacial properties between the copper mesh and the insulated adhesive layer are attributed to the aggravated LS damage area of the copper mesh, whereas the gas explosion is the key factor contributing to the increased damage in the CFRC-Al specimens. In addition, an increase in the adhesive layer thickness intensified the LS damage in the CFRC-Cu specimens but reduced the damage in the CFRC-Al specimens after WA.

Evaluating interfacial bonding quality of multilayered structure based on ultrasonic testing technology

An ultrasonic evaluation method of interfacial bonding quality from layered structures is proposed for enhancing the testing accuracy. The ultrasonic reflection and transmission characteristic is theoretically analyzed, which focus on the different quality of the single and double bonding interface with spring-type. The reflection coefficient and transmission coefficient mathematic models, which include multiple parameters, are derived from the transfer matrix. Taking the first, second, and the double bonding interface as the research objects, respectively, two types of resonant frequencies have been presented by numerical solving the model, namely, the first type resonance frequency (RFI) and the second type resonance frequency (RFII). The results show that the interval of the RFⅠ is related to medium thickness of the maximum acoustic impedance. Similarly, the interval of the RFⅡ depends on other layers’ thickness. In addition, the transmission coefficient shows a change in different trends with the bonding interface gradually tending to rigid. When the adhesive layer thickness is sufficiently small compared with the wavelength, the reflection coefficient shows many local minima points at a certain frequencies range, the frequency of local minimum point increases with the increase of the stiffness coefficient. The experimental results are in good agreement with the numerical solution results and finite element analysis results.

Micro-Transfer Printing for Heterogeneous Integration of GaN and GaAs HEMTs

Here, we use the micro-transfer printing technique to demonstrate the device-level heterogeneous integration of two solid-state RF device technologies on the same interposer: GaN and GaAs high-electron-mobility transistors. The devices are released from their growth substrate using an epitaxial sacrificial layer while a thin polymer adhesion layer facilitates a strong bond between the target substrate and the compound semiconductor devices, allowing for post-transfer microfabrication processing. Transmission electron microscopy reveals no voids at the device/interposer interface and a polymer adhesion layer thickness of 5 ± 2 nm. No significant degradation in dc electrical characteristics is observed after device transfer for either device technology. Improvement in thermal performance of GaN devices was demonstrated when transferred to a diamond substrate, even with the thin polymer adhesion layer at the device/interposer interface, illustrating a pathway for enhanced thermal management for GaN and other high-output-power density semiconductor technologies. The ability to combine various solid-state technologies at the device level with high density provides an approach to meet next-generation demands for RF and mixed-signal circuits.

Structural and Mechanical Investigation of Class I Biomimetic Composite Dental Filling by X-ray Computed Tomography, Scanning Electron Microscopy, and Microtensile Bond Strength Testing

Nowadays, short fiber-reinforced composites are broadly used in modern restorative dentistry. The tensile strength, Young's modulus, density, and polymerization shrinkage of these materials are developed to mimic the original teeth tissue best. The shrinkage, however, will occur during any polymerization process, which can cause residual stress and gap formation between the tooth and the filling. These can lead to the propagation of cracks, reduction in the adhesive bond strength, or even cause separation in the restoration. During this research, a biomimetic dental restoration was created on a surgically removed third molar with EverX short-fiber reinforced dental composite by bulk-filling technique. The restored tooth sample was examined by X-ray computed tomography to obtain a 3D image of the whole restoration. The volume of the used adhesive, the material discontinuities, and internal cavities were determined. A cut-out slice was further investigated by scanning electron microscopy to examine the adhesive layer thickness, the gap formation, and the quality of the filling. Finally, microtensile specimens were machined to evaluate the bond strength between the tooth dentin and the filling material.

Study of the effects of deformation rate and adhesive layer thickness under impact loading on parameters of adhesive joints in a vehicle

BACKGROUND: At the present time, new technologies of joints adhesive joints are used more and more widely along with spot welding in domestic and foreign vehicles. Study of the joint strength and the influence of deformation rate and the adhesive layer thickness under impact loading on the parameters of the joint in a vehicle is a relevant technical task.&#x0D; AIMS: Study of the influence of deformation rate and the adhesive layer thickness on the adhesive joint parameters (strength, deformation, etc.) under impact loading as well as evaluation of the efficiency of the proposed modified calibration method for the adhesive layer model on the example of tubular structure, which is often used in the strength elements of a vehicle.&#x0D; METHODS: Experimental studies were carried out with impact loading at the speed of 6.66 m/s (the axial im-pact) and 6.87 m/s (the side impact) with the mass of 22.3 kg. Simulation of operating conditions was performed in the LS-Dyna software that made possible to study the stress-strain states (SSS) of adhesive-bonded tubular structures and to estimate the simulation error.&#x0D; RESULTS: Based on experimental and calculated results, the length of the adhesive layer failure under the impact loading in the steel structures bonded with the Henkel EP 5055 adhesive is shorter in the joints with the 0.5 mm thick adhesive layer than in the joints with the 1 mm thick adhesive layer. The total deformation of the bonded structure at the side impact loading for the 1 mm thick adhesive layer is less than for the 0.5 mm thick layer, as the adhesive layer absorbs some of the energy. For the axial impact loading, the differences are insignificant. Errors of adhesive joint simulation under impact loading have been reduced significantly (by 15%) with using the proposed modified method of calibrating the adhesive layer properties considering the influence of the deformation rate and the adhesive layer thickness in the finite element model.&#x0D; CONCLUSIONS: The practical value of the study lies in the proposed modified model, considering the influence of the deformation rate and the adhesive layer thickness under impact loading on the joint parameters and making possible to improve simulation accuracy, as well as in recommendations for the best value of adhesive joint properties in adhesive-bonded vehicle structures.

Experimental and numerical investigation of the damping properties of adhesively bonded tubular steel joints

ABSTRACT A large number of structures in various fields are repeatedly subjected to dynamic loading during their lifetime. To avoid or reduce vibration amplitudes possibly occuring, the use of vibration damping measures is necessary. Due to their inherent material damping, viscoelastic adhesives show a potential to reduce the dynamic effects of structures. This has not yet been comprehensively investigated for adhesively bonded joints. This paper reports on experimental and numerical investigations of damping properties of adhesively bonded tubular steel joints in a scale relevant for construction industry and thus represents a fundamental data set. Different adhesive joint geometries and test parameters were investigated experimentally and their influence on the damping properties of adhesively bonded specimens is discussed and evaluated. The test results show that the damping properties of adhesively bonded joints can be enhanced by increasing the adhesive layer thickness and reducing the overlap length. In addition, the damping properties of the test specimens increase with a rise in the stress on the adhesive layer. The influence of the test frequency on the loss factor is of secondary importance. Furthermore, material models of the adhesives used were developed and validated successfully on the basis of the experimental test result presented.

Damping Properties of Large-Scale Overlap Joints Bonded with Epoxy Hybrid Resin or Polyurethanes: Experimental Characterisation and Analytical Description

Structures in various industries are exposed to dynamic loads. The dissipative properties of adhesively bonded joints can contribute to the damping of dynamically stressed structures. Dynamic hysteresis tests are carried out to determine the damping properties of adhesively bonded overlap joints by varying the geometry and test boundary conditions. The dimensions of the overlap joints are full-scale and thus relevant for steel construction. Based on the results of experimental investigations, a methodology is developed for the analytic determination of the damping properties of adhesively bonded overlap joints for various specimen geometries and stress boundary conditions. For this purpose, dimensional analysis is carried out using the Buckingham Pi Theorem. In summary, it can be stated that the loss factor of adhesively bonded overlap joints investigated within this study is in the range between 0.16 and 0.41. The damping properties can particularly be increased by increasing the adhesive layer thickness and reducing the overlap length. The functional relationships of all the test results shown can be determined by dimensional analysis. An analytical determination of the loss factor considering all identified influencing factors is enabled by derived regression functions with a high coefficient of determination.