Adhesive Bond Strength Research Articles

Effect of erosive challenge and cigarette smoke on dentin microhardness, surface morphology and bond strength

Objective: This study aimed to evaluate the surface microhardness and morphology, as well as the microshear bond strength of a self-etching adhesive (Clearfil SE, Kuraray) to eroded dentin, exposed or not to cigarette smoke. Forty dental crowns were divided into 4 groups (n = 10): no treatment (control) (C); erosion (E); erosion + cigarette smoke exposure (ES); cigarette smoke exposure (S). Samples were prepared through third molars polishing until dentin exposure, followed by crown section. Erosive cycles were performed 5 times/day for 30 s at 60 min intervals. Cigarette smoke was produced with twenty cigarettes/day, during 5 days. Microhardness was evaluated initially and after the treatments. Microshear bond strength was tested after the treatments and dentin restoration with flow composite. Failure patterns and dentin morphology was evaluated by Scanning Electron Microscopy. Microshear bond strength data was submitted to two-way ANOVA, microharness test was adjusted by gamma distribution to be a non-parametric analyses (p=0.05), and surface morphology as qualitative analyses. Loss percentage of microhardness was observed only in groups submitted to erosion. Bond strength was statistically similar between all groups. The most prevalent failure pattern was of adhesive type. Morphological analysis of dentin showed obliterated tubules in groups submitted to cigarette smoke exposure. Cigarette smoke exposure did not promote any effect in the percentage of microhardness loss, as in sound dentin as in eroded dentin. Cigarette smoke, erosion, and association of both, did not alter the bond strength of self-etching adhesives to dentin.KeywordsBond strength; Cigarette Smoke; Dental erosion; Microhardness; Self-etching adhesives.

Thermal Oxide Layer Enhances Crystallinity and Mechanical Properties for Plasma-Sprayed Hydroxyapatite Biomedical Coatings.

The stability of plasma-sprayed hydroxyapatite (HA) coatings on metallic implants in vivo remains a significant challenge for load-bearing orthopedic implants despite their excellent mechanical and osteoconductive properties. This study focuses on oxide layer formation on the surface of Ti6Al4V samples through furnace heating at 600, 700, and 800 °C for 10 min for optimization of the most effective oxide layer to increase plasma coating crystallinity and improve plasma coating bond strength with the metal surface. The 800 °C heat treatment shows an effective oxide layer which increases coating crystallinity from 64 to 75% and coating adhesive bond strength from 25.9 ± 2.3 to 30.7 ± 1.1 MPa, while simultaneously reducing the dissolution rate of HA coatings. The addition of biologically relevant dopants, MgO and SiO2, show negligible effects on crystallinity and adhesive bond strength on plasma-sprayed HA coatings and additionally show an enhancement effect on osteoblast proliferation and differentiation. Moreover, the inclusion of these additivess shows an increase in osteogenesis in a rat distal femur model after 6 and 10 weeks of implantation. Overall, this study provides a direct solution to improve the crystallinity, adhesive bond strength, and osteogenic properties of plasma-sprayed HA coatings on orthopedic implants that is more manufacturable and translational from research to an industrial scale.

Efficacy of chlorhexidine, Er Cr YSGG laser and photodynamic therapy on the adhesive bond integrity of caries affected dentin. An in-vitro study.

To evaluate the adhesive bond integrity (shear bond strength-SBS) of composite resin bonded to carious dentin using chlorhexidine gluconate (CHX), Er,Cr:YSGG laser (ECYL) and photodynamic therapy (PDT). Thirty carious and ten non-carious mandibular teeth were collected through non-traumatic extraction. All samples were embedded in polyvinyl cross-sections to the cemento-enamel junction. The preparation of caries-affected dentin was performed by grinding the specimens using silicon carbide discs. All specimens were randomly allocated in to four groups (n = 10). Group 1, non-affected dentin with no disinfection; Group 2, caries affected dentin treated with 2% CHX; Group 3, affected dentin disinfected with PDT [100 mg/L methylene blue solution (MBS) and Diode laser]; Group 4, affected dentin treated with ECYL. Self-etch adhesive was smeared on all specimens for 10 s and photopolymerized for 10 s. All specimens were placed in an incubator with humid environment for 24 h at 37 °C followed by positioning in universal testing machine for SBS testing. Failure mode examination of debonded samples was performed by a stereomicroscope. Analysis of variance (ANOVA) was used for inter group comparison through mean and standard deviation of each group. For multiple group comparison Tukey HSD was employed. Level of significance was established at p < 0.05. The highest SBS value was observed in group 1 (24.98 ± 1.59 MPa). Whereas, the lowest bond strength was displayed by group 3 (14.22 ± 1.40 MPa) specimens. Lased dentin in group 4 (15.89 ± 3.22 MPa) exhibited SBS values comparable to group 3 (14.22 ± 1.40 MPa). Group 2 (CHX-18.25 ± 1.29 MPa) exhibited statistically significant difference compared to all experimental groups (p < 0.05). Adhesive bond strength of disinfected carious dentin was higher with CHX treatment as compared to Photodynamic therapy and Er,Cr: YSGG laser treatment. Carious dentin showed lower bond strength to composite resin as compared to non-carious dentin.

Evaluation of bond strength of molar orthodontic tubes subjected to reinforcement with flowable and bonding resins

The goal was to evaluate the adhesive shear bond strength (SBS) of orthodontic tubes bonded to molar teeth and reinforced with Transbond XT (3M Science, St. Paul, MN, USA) and flowable resin. In all, 120molar teeth, previously extracted from patients with amean age of30 were included. Orthodontic molar tubes were bonded on the vestibular surface of these teeth with one of two types of adhesive (Transbond XT [3M Science, St. Paul, MN, USA] or Orthobond [Morelli, Sorocaba, Brazil]). Each of these groups was subsequently divided into four further groups: control and those subjected to the use of resin reinforcement on the occlusal surface of the bonded tubes with one of three materials (Transbond XT, Tetric N Flow [Ivoclar Vivadent, Ellwangen, Germany], Z350 Flow [3M Science, St. Paul, MN, USA]). SBS and adhesive remnant index tests were performed to evaluate bond strength and type of fracture of the tubes bonded with the different methods. The use of resin reinforcement with Transbond XT significantly increased the SBS of tubes bonded with both materials. Flowable composites did not increase the SBS when used as areinforcement. Less than 50% of the adhesive remained on the vestibular surface after the SBS test in most samples of all groups. Transbond XT orthodontic adhesive and Orthobond adhesive had appropriate bonding strengths for clinical use. Furthermore, the use of aresinous reinforcement with Transbond XT significantly increased the SBS of tubes bonded. However this technique with flowable adhesives (Tetric N Flow and Z350 Flow) did not significantly increase SBS when orthodontic tubes were bonded with Transbond XT or Orthobond.

In Vitro Study on the Effect of a New Bioactive Desensitizer on Dentin Tubule Sealing and Bonding.

Bioactive mineral-based dentin desensitizers that can quickly and effectively seal dentinal tubules and promote dentin mineralization are desired. This in vitro study evaluated a novel nanohydroxyapatite-based desensitizer, Predicta (PBD, Parkell), and its effect on bond strength of dental adhesives. Human dentin discs (2-mm thick) were subjected to 0.5 M EDTA to remove the smear layer and expose tubules, treated with PBD, and processed for surface and cross-sectional SEM examination before and after immersion in simulated body fluid (SBF) for four weeks (ISO 23317-2014). The effects of two dental desensitizers on the microshear bond strength of a universal adhesive and a two-step self-etch system were compared. SEM showed coverage and penetration of nanoparticles in wide tubules on the PBD-treated dentin at the baseline. After four weeks in SBF, untreated dentin showed amorphous mineral deposits while PBD-treated dentin disclosed a highly mineralized structure integrated with dentin. Desensitizers significantly reduced microshear bond strength test (MSBS) of adhesives by 15–20% on average, depending on the bonding protocol. In conclusion, PBD demonstrated effective immediate tubules sealing capability and promoted mineral crystal growth over dentin and into the tubules during SBF-storage. For bonding to desensitizer-treated dentin, a two-step self-etching adhesive or universal bond with phosphoric acid pretreatment are recommended.

Effect of double-layer application on the early enamel bond strength of universal adhesives.

The present study aimed to investigate the changes in the enamel bond strengths of universal adhesives in the early phase of specimen creation and evaluate the effect of double-layer application on enamel bond effectiveness using different etching modes. Four universal adhesives, namely Clearfil Universal Bond Quick, G-Premio Bond, Scotchbond Universal, and Tokuyama Universal Bond, were used. Clearfil SE Bond two-step self-etch adhesive system was used as a comparison. Fifteen specimens per group were used for determining the shear bond strength (SBS) to bovine enamel in the etch-and-rinse or self-etch mode. The adhesive was applied to specimens in accordance with the manufacturers' instructions (single-layer application), or the adhesive was applied twice (double-layer application). The bonded specimens were stored in distilled water at 37°C for 5min or 1, 6, 12, or 24h before SBS testing. The flexural properties of the resin composite Clearfil AP-X were measured for the same storage periods. All universal adhesives exhibited increased SBS values with prolonged storage periods regardless of the application technique or etching mode used. Double-layer application was associated with higher SBS values than single-layer application for most universal adhesives over the same storage period. Phosphoric acid pre-etching and double-layer application of universal adhesives resulted in increased enamel bond strength in the early phase of specimen bonding. Care should be taken when using universal adhesives in the self-etch mode for enamel bonding because the enamel adhesion is sensitive to the duration after filling.

Air-blowing strategies for improving the microtensile bond strength of one-step self-etch adhesives to root canal dentin.

The effect of different air-blowing strategies using a prototype of a newly developed clinically applicable warm air-blowing device on the microtensile bond strength (μTBS) of one-step self-etch adhesives (1-SEAs) to human root-canal dentin was evaluated. Post cavities (8 mm depth, 1.5 mm diameter) were prepared and bonded with four 1-SEAs. Air-blowing was performed using normal air (23±1°C) for 10 or 20 s; warm air (60±1°C) for 10 or 20 s; or their combination for 10 s (5 s normal, 5 s warm) or 20 s (10 s normal, 10 s warm). After filling with corresponding core materials and 24-h water storage, μTBS test was performed. For three of the 1-SEAs, combined air-blowing for 20 s significantly increased μTBS compared to other air-blowing strategies (p<0.05). This suggests that the combination of normal and warm air-blowing for 20 s can enhance solvent evaporation from 1-SEAs, thus resulting in their improved bonding performance to root-canal dentin.

Modelling of membrane bonding response: part 2 finite element simulations of membrane adhesion tests

ABSTRACT The adhesive bonding strength of the membrane layers between the asphalt concrete surface layers and the decks of steel bridges has a strong influence on the fatigue life of orthotropic steel deck bridges (OSDBs). The interfacial properties between the membrane and the layers bonded to it have not been extensively studied in the current orthotropic steel deck bridge system. For the adequate characterisation of the adhesive-bonding strength of various membranes and surrounding materials on OSDBs and for the collection of the necessary parameters for finite element model, details of the membrane adhesion test (MAT) are introduced and simulated by using the adhesive traction-separation interface element which was developed in a companion paper to this contribution (Liu, X., Kasbergen, C., Li, J., & Scarpas, A. (2019). Modelling of membrane bonding response: part 1 development of an adhesive contact interface element. International Journal of Pavement Engineering). Parametric studies of the adhesive contact element utilised for modelling the membrane bonding layer in the MAT test have been performed on the basis of the combination of different critical strain energy release rates and the characteristic opening length in the constitutive model. Comparison of membrane deformation profiles and the in-time debonding force distribution between experimental observations and finite element simulations have been presented.

Standard Test Method ASTM D 7998-19 for the Cohesive Strength Development of Wood Adhesives.

The properties of cured wood adhesives are difficult to study because of the loss of water and other components to the wood, the influence of wood on the adhesive cure, and the effect of adhesive penetration on the wood interphase; thus, normal testing of a neat adhesive film is generally not useful. Most tests of wood adhesive bond strength are slow, laborious, can be strongly influenced by the wood and do not provide information on the kinetics of cure. Test method ASTM D 7998-19, however, can be used for fast evaluation of the strength of wood bonds. The use of a smooth, uniform, and strong wood surface, like maple face-veneer, and sufficient bonding pressure reduces the adhesion and wood strength effects on bond strength. This method has three main applications. The first is to provide consistent data on bond strength development. The second is to measure the dry and wet strengths of bonded lap shear samples. The third is to better understand the adhesive heat resistance by quickly evaluating thermal sensitivity and distinguishing between thermal softening and thermal degradation.

Enhancement of strength of adhesive bond between wood and metal using atmospheric plasma treatment

Combinations of wood and metal are interesting hybrid composite materials, joining together the low density of wood with the stiffness and strength of metals. Different types of adhesives are used to connect wood and metal elements, but the compatibility between adhesives used and load-bearing materials must be sufficient, which often is challenging. In adhesive bonding technology, surface treatments are a crucial step in the process. In this study, an atmospheric plasma discharge was employed to enhance the adhesion strength of joints between common beech (Fagus sylvatica L.) wood, metals (steel and aluminum alloy), and four different types of adhesives. The optical properties of plasma discharges and its influence on treated substrates’ surface morphology depended on the inherent properties of the treated materials. X-ray photoelectron spectroscopy revealed the surface oxidation of all the materials after plasma treatment. Consequently, the surface free energy of all materials increased as well. The positive effect of the plasma treatment on the tensile shear strength of single-lap joints shows a high potential of atmospheric plasma treatment technology for enhancement of adhesives strength of joints combining wooden elements, wood and steel, or wood and aluminum alloys. In addition to that, expensive epoxy and polyurethane adhesives could be replaced by more affordable polyvinyl acetate and melamine-urea-formaldehyde adhesives, and still perform at equal levels if the plasma was applied prior to bonding.

Influence of Prolonged Dental Bleaching on the Adhesive Bond Strength to Enamel Surfaces.

The objective of this in vitro study was to assess the influence of prolonged bleaching pre- and postrestoration on the bond strength (microshear) to enamel using 4% hydrogen peroxide (PH4). In the postrestorative bleached specimens evaluation, the composite cylinders were assembled after bleaching, while in the prebleached specimens, the cylinders were assembled before. Therefore, in the postbleached specimens, 60 bovine teeth were randomly assigned as follows: G1: control; G2: 14 days bleaching before bond strength (BS) testing; G3: 21 days; and G4: 28 days. In prebleached specimens, 180 bovine teeth were randomly assigned as follows: G1: control; G5: 14 days bleaching, storage in artificial saliva (AS) for 24 h before BS testing; G6: 14 days beaching, AS storage for 7 days before BS testing; G7: 21 days bleaching, AS storage for 24 h before BS testing; G8: 21 days bleaching, AS storage for 7 days before BS testing; G9: 28 days bleaching, AS storage for 24 hours before BS testing; and G10 : 28 days bleaching, AS storage for 7 days before BS testing. The results were submitted to ANOVA one-way (postrestoration bleaching) and two-way (prerestoration bleaching) and Tukey's post hoc test (p ≤ 0.05). In the postrestoration bleaching, no statistical difference between times was found. However, when bleached groups were compared to the control (G1), an expressive difference was detected (p ≤ 0.0001). For prerestoration bleaching, all experimental groups were statistically different from G1 (p ≤ 0.05), except G6 (p ≥ 0.01), and for G5 and G6, statistical differences were found (p ≤ 0.01). There were no significant differences between G7 and G8 and between G9 and G10, regardless of the AS storage times (p ≥ 0.05). It was concluded that prolonged bleaching with PH4 decreased adhesion resistance regardless of the moment of the bleaching (post- and prerestoration bleaching).

A procedure to assess disbond growth and determine fatigue life of bonded joints and patch repairs for primary airframe structures

This paper assesses the suitability of a damage slow growth management strategy to bonded joints or patch repairs of primary aircraft structures. The entire process of a disbond crack growth from initiation to the ultimate failure of a typical double lap metallic joint is investigated. The residual static strength of the joint as function of disbond crack length is established using the finite element method with adhesive element failure criteria and a progressive failure analysis. For a joint having sufficient static strength safety margin under a typical fatigue loading that would propagate disbond crack, a finite element fracture mechanics analysis indicates that the disbond growth would be stable in a significant length range of the disbond crack, initiated from either “disbond tolerant zone” or “safe-life zone”. The analysis further suggests that for local (part width) disbond, due to load redistribution effect the disbond growth rate would be reduced as the disbond propagates. These results suggest the slow growth approach would indeed be feasible. With the above analyses, the framework to implement the slow growth approach, predict allowable fatigue life and determine inspection interval, in accordance with the guidance provided in FAA AC 20-107B [1], is established. Furthermore, this study assesses the effect of rigidity imbalance between inner adherend and outer adherend and shows how varying the adherend thickness could affect the adhesive bond strength and disbond growth rate. This information would be useful in design of validation experiment.

Effects of phase-inversion waterborne epoxy resin on properties of cold patch waterborne epoxy emulsified asphalt

In order to evaluate effects of waterborne epoxy resin prepared by the phase-inversion method (phase-inversion waterborne epoxy resin) on properties of waterborne epoxy emulsified asphalt for cold patch engineering of asphalt pavement, a series of methods for evaluating properties of emulsified asphalt and casting resin were used. Results show that, with an increase in waterborne epoxy resin content, penetration, ductility, surface curing time of waterborne epoxy emulsified asphalt decrease and its adhesion degree, shear strength and bond strength increase. Moreover, its penetration, ductility and adhesion degree remain unchanged when the content of waterborne epoxy resin exceeds 20%, and its shear strength and bond strength increase most remarkably when the content of waterborne epoxy resin increases from 10% to 20%. The test results are explained by the surface fluorescent micromorphology of cured waterborne epoxy emulsified asphalt that, with the increase in waterborne epoxy resin content, epoxy resin particles firstly appear as segregated spots, and then change from spotted status to clustered status, and the epoxy resin phase gradually becomes a continuous phase. In conclusion, phase-inversion waterborne epoxy resin has effects on properties of the cold patch waterborne epoxy emulsified asphalt, and recommended content of waterborne epoxy resin is 20%.

Study of temperature impact on the behaviour of fibre polymer materials′ and their adhesive bonds

A study that provides a complex assessment of the influence of high temperature on the behaviour of textiles and changes in peeling strength of adhesive bonds due to temperature is not available. Thus, the aim to investigate the influence of temperature on the structure of polyester/elastane knitted materials as well as on peeling strength of their bonds was raised. Results revealed that peeling strength of the bonds depends on materials’ structure and bonding temperature. TGA data revealed that thermal decomposition temperature for all investigated materials is higher than 300 °C. DSC analysis showed that textiles do not melt at lower than 200 °C. Thus, it was proven that the determined tendency of bond peeling strength decreases due to increase in bonding temperature up to 170 °C compared to 160 °C are more related to material ability of easily absorbing the highly melted adhesive. 150 °C temperature is optimal for majority of the investigated textiles.

Influence of Natural Zeolite and Paraffin Wax on Adhesion Strength Between Bitumen and Aggregate

Asphalt mixture that is used for the construction of flexible pavements is mainly composed of two constituents i.e. bitumen and aggregate. Sturdy adhesion among bitumen and aggregate is the sign of durability of asphalt pavements. Adhesion is considered as one of the most important factors for sustainable asphalt pavement. This is the motive why its miles utmost important to deeply understand the phenomenon of adhesion considering the effect of alternate in temperature, moisture conditions. In this study softer binder 80/100 was selected that has less adhesion compared to hard pen grades. Limestone aggregates which is commonly used for the construction of asphalt pavements has also been selected. Two types of modifiers (Zeolite and Paraffin Wax) were selected because of the extensive use in asphalt foaming and the polymer modified asphalt mixtures as temperature reducing agent. To investigate the strength of adhesive bond, Bitumen Bond Strength (BBS) was performed at different temperatures, in dry, and wet conditions. To quantify the effect of modifiers on penetration grade and softening point conventional testing is performed. For performance grading, the PG test was performed using Dynamic Shear Rheometer. The comparisons were developed among pull of tensile strength at dry and after 72hrs water conditioning while preserving the temperature at 25 .To check the effect of temperature BBS is performed at 15 . The results illustrate that 2% zeolite shows best results in terms of adhesion and performance grade while Paraffin wax has less adhesion and poor performance grade.

Correlation of Interface Microstructural Features with the Adhesive Bonding Strength of Galvannealed Interstitial-Free Steel

Flaking of galvannealed steel due to interfacial bond failure during press-forming results in a deterioration in product quality and reduced productivity. To solve this problem, an understanding of bonding at the interface must be gained in terms of the microstructure. In this research, the relationship between coating adhesion strength and the evolution of interface microstructure was investigated using an interstitial free steel sheet. Hat channel drawing with a bead machine and stud pin tests were used to measure the flaking resistance and adhesive bond strength, respectively. A strong relationship was found between flaking resistance and interfacial bond strength. High bond strength samples exhibited two distinctive microstructures, Zn-penetrated grain boundary, and rough, island-like knoll, with the knoll always surrounded by the grain boundaries. The rough knoll, with etch pits on the top, formed underneath a crater, and a deep pit was observed at the grain boundary. After stud pin testing, coating residues remained mostly on the Zn penetrated and rough knoll substrates, indicating strong coating adhesion reinforced by a mechanical interlocking effect that originated from the two distinctive microstructures.

Synthesis and performance evaluation of nanocomposite soy protein isolate/carbon nanotube (SPI/CNTs) adhesive for wood applications

In this article, effect of the incorporation of carbon nanotubes (CNTs) into soy-based adhesive, obtained from soy protein isolate (SPI), on the performance of the nanocomposite adhesive is presented. Multifunctional and exceptional properties of carbon nanotubes (CNTs) in nanofiller in polymer matrix were explored in this study to develop nanocomposite soy-based adhesive with improved shear strength and water resistance. Consequently, nanocomposite SPI/CNT adhesives having different CNT loading were synthesized and evaluated. Morphology, thermal stability and chemical functionalities of the synthesized nanocomposite adhesives were checked using scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy, respectively. The bond strength test of the adhesives was carried out according to European standards, EN-204 and EN-205. The results showed that CNTs improved the shear strength of the nanocomposite SPI/CNT adhesive at reduced percentage loading. About 100% increase in the shear strength and water resistance was recorded for the nanocomposite SPI/CNTs adhesive when compared with an alkaline modified adhesive without carbon nanotubes. The shear strength of the nanocomposite adhesive increased from 3.48 MPa (adhesive without CNTs) to 6.91 MPa (adhesive with 0.3 wt% CNT loading) and then decreased afterwards as the CNT loading was increased beyond 0.3%. Enhanced shear strength of soy-based adhesives using different fillers has been reported in the literature, but at relatively high loading of the filler. In this study, relatively small amount of CNTs (0.3%) has shown a substantial enhancement in shear strength as compared to other fillers. It is expected that the newly developed adhesive could pave the way to solving the challenge of low shear bond strength and poor water resistance of soy-based adhesives for wood applications in the industry.

Analysis of the influence of a new type of buccal tube base mesh design on the adhesive layer stress distribution and bond strength

The three-dimensional finite element method was used to analyse the effect of changing the buccal tube baseplate shape on the stress magnitude and distribution at the interface between the buccal tube and the adhesive layer in a buccal tube-adhesive layer-tooth continuum under shear and tensile loads. A stress regression analysis was used to select the optimum mesh design and was verified by in vitro bond strength testing. This study involved buccal tubes with triangular mesh bases (100–400 µm mesh lengths, 100–200 µm mesh spacings, and 0, 45 and 90° angles) and a traditional quadrilateral mesh base. A finite element model of the buccal tube, adhesive layer and tooth were established. The stresses in the adhesive layer-buccal tube interface were recorded under mesial loads, distal loads, vertical loads and tensile loads. The average bond strength was measured by debonding the buccal tube with a universal testing machine and crosshead at a speed of 0.5 mm/min. Increasing the mesh length and mesh spacing decreased the von Mises stress and the first principal stress at the triangular mesh base-adhesive interface. Further analysis showed that the lowest stress and maximum mean bond strength were exhibited by the triangular mesh base (400 µm mesh length, 200 µm mesh spacing). Changes in the shape and size of the base grids affected the stress magnitude and distribution at the adhesive layer interface. The optimal triangular mesh base design in this study provides new ideas for clinical applications.

Вероятностное моделирование адгезионно-латентного взаимодействия структурных элементов композиционных материалов

A block diagram of the interaction of the main elements of polymer composite materials and a probabilistic model of their functioning are proposed. The double role of the adhesion factor of polymer composite materials is shown and the possibility of its optimization is established. The kinetics of fracture of polymer composite materials is analyzed taking into account the strength of adhesive bonds and prospects for further research are outlined.

Influence of Embedding Fiber Optical Sensors in CFRP Film Adhesive Joints on Bond Strength.

The increasing utilization of carbon fiber reinforced plastic (CFRP) in the aeronautical industry calls for a structural health monitoring (SHM) system for adhesively bonded CFRP joints. Optical glass fiber with inscribed fiber Bragg gratings (FBGs) is a promising technology for a SHM system. This paper investigates the intrusive effect of embedding optical glass fibers carrying FBGs on adhesive bond strength and adhesive layer thickness and quality. Embedding the optical glass fibers directly in the adhesive bond has the advantage of directly monitoring the targeted structure but poses the risk of significantly reducing the bond strength. Optical glass fibers with different cladding diameters (50, 80, 125 µm) and coating types (polyimide, with a thickness of 3−8 µm, and acrylate, with a thickness of ~35 µm) are embedded in structural and repair film adhesives here. Without embedded optical glass fibers, the film adhesives have an adhesive layer thickness of ~90 µm (structural) and ~100 µm (repair) after curing. The intrusive effect of the fiber embedding on the adhesive bond strength is investigated here with quasi static and fatigue single lap joint (SLJ) tensile shear tests. Also, the influence of hydrothermal aging procedures on the quasi static tensile shear strength is investigated. It is found that optical glass fibers with a total diameter (glass fiber cladding + coating) of ~145 µm significantly reduce the quasi static tensile shear strength and increase the adhesive layer thickness and number of air inclusions (or pores) in the structural film adhesive joints. In the repair adhesive joints, no significant reduction of quasi static tensile shear strength is caused by the embedding of any of the tested fiber types and diameters. However, an increase in the adhesive layer thickness is detected. In both adhesive films, no effect on the quasi-static tensile shear strength is detected when embedding optical glass fibers with total diameters <100 µm. The applied aging regime only affects the repair film adhesive joints, and the structural film adhesive joints show no significant reduction. A polyimide-coated 80 µm optical glass fiber is selected for fatigue SLJ tensile shear tests in combination with the more sensitive structural film adhesive. No significant differences between the S-N curves and tensile shear fatigue strength of the reference samples without embedded optical fibers and the samples carrying the polyimide-coated 80 µm optical glass fibers are detected. Thus, it is concluded that the influences of embedding optical glass fibers with total diameters <100 µm on the fatigue limit of the tested film adhesive joints is negligible.