Interfacial Bond Strength Research Articles

Short- and Long-Term Dentin Bond Strength of Bioactive Glass-Modified Dental Adhesives.

This study investigated the short- and long-term effects of dental adhesives doped with nano-sized bioactive glass 45S5 (BAG) on the resin–dentin interfacial bond strength. Two etch-and-rinse adhesives (Adper Scotchbond Multi-Purpose (ASB) and Solobond Plus (SB)) and one self-etch adhesive (Clearfil SE Bond (CF)) were doped with different concentrations of BAG (5, 10, and 20 wt%). The unmodified (0 wt% BAG) commercial adhesives served as control groups. Dentin of 120 molars (n = 10 per group) was treated with the different adhesives, followed by buildups with a conventional composite restorative material. From each tooth, 14 sticks were prepared for micro-tensile bond strength (µTBS) testing. The sticks were stored in simulated body fluid at 37 °C and tested after 24 h or six months for µTBS and failure mode. Data were analyzed using Kruskal–Wallis tests in combination with post-hoc Conover-tests and Wilcoxon signed-rank tests at a level of significance of α = 0.05. After 24 h and six months, both etch-and-rinse adhesives with a low BAG content (up to 10 wt% for ASB and 5 wt% for SB) showed similar µTBSs as their respective control groups (0 wt% BAG). CF showed a significant decrease in µTBS even after addition of 5 wt% BAG. At a high concentration of added BAG (20 wt%), all three adhesives showed a significant decrease in µTBS compared to the unmodified controls. The CF control group showed significantly lower µTBS after 6 months of storage than after 24 h. In contrast, the µTBS of all CF groups modified with BAG was unaffected by aging. In conclusion, the tested etch-and-rinse adhesives can be modified with up to 5 wt% (SB), or 10 wt% (ASB) of BAG without reducing their short- and long-term dentin bond strength. Moreover, the addition of nano-sized BAG may prevent long-term bond strength deterioration of a self-etch adhesive.

Role of sizing agent on the microstructure morphology and mechanical properties of mineral-impregnated carbon-fiber (MCF) reinforcement made with geopolymers

This report deals with the influence of different sizing agents on carbon fiber (CF) heavy tows towards their impregnation with a geopolymer (GP) suspension and resulting properties of mineral-impregnated carbon-fiber composites (MCF) produced in an automated, continuous process. Three different commercial CFs were investigated after treatment with either thermoplastic, epoxy, or vinyl-ester sizing agents and then compared to unsized CFs. During impregnating, diverse yarn-spreading behavioral modes and degrees of wetness were observed, indicating different degrees of impregnation, both in quality and quantity. All sizing agents decreased the hydrophobic nature of unsized CFs significantly. Supported by microscopic investigation, water contact angle measurement, and thermal gravimetric and mercury intrusion porosity, the epoxy sizing showed the best fiber-matrix distribution over the cross-section and a dense microstructure. Moreover, in single-fiber pullout tests each sizing brought about a significant increase in maximum pullout force, indicating enhanced bond between fiber and matrix. This is attributed to more intense interaction in the interfacial region, fully corroborating the topological characteristics obtained in microscopic analysis. With higher interfacial bond strength, the thermoplastic sizing enabled the highest tensile properties of MCF despite slightly less impregnation quality in comparison with epoxy-sized samples.

Ensemble learning based approach for FRP-concrete bond strength prediction

Nowadays, externally bonding fiber reinforced polymer (FRP) plates or sheets have become a major maintenance approach for aged reinforced concrete flexure structures. However, the capacity of strengthend structure cannot be precisely estimated as a result of the critical FRP-concrete interfacial (FCI) bond strength unpredictable. In order to solve this issue, many experimental studies have been carried out with corresponding emipirical models proposed. Due to limited experiment samples, these models were found more or less lacking the generalization ability. Under this circumstance, in this study, an ensemble learning algorithm “gradient boosted regression trees” (GBRT) was employed to develop a prediction model for FCI bond strength prediction based on a collected comprehensive database containing 520 tested samples. The model’s performance has been thoroughly compared with the representative empirical models and the common utilized machine learning algorithms. The rationality of this model has also been discussed through feature importance analysis. The results showed that the model in this study exhibits the highest accuracy and is proven to be feasible for predicting FCI bond strength in actual practice.

Experimental and Numerical Study on Interface Bond Strength and Anchorage Performance of Steel Bars within Prefabricated Concrete.

This study investigates the interface bond strength and anchorage performance of steel bars within prefabricated concrete. Twenty-two specimens were designed and manufactured to study the interface bond behavior of deformed and plain steel bars under a larger cover thickness. Diameter of steel bars, strength grade of concrete, and anchorage length were considered influential factors. The finite element method (ABAQUS) was used for the validation of experimental results. The interface bond’s failure mechanism and the anchorage length in the prefabricated concrete under different concrete strength levels were explored and compared to national and international codes. A suitable value of the basic anchoring length for the prefabricated structure was recommended. The results show that the interface bond strength of prefabricated bridge members is directly proportional to the strength grade of the concrete, inversely proportional to the reinforcement diameter, and less related to anchorage length. The effect of the cover thickness of the surrounding concrete is negligible. Conversely, the bearing capacity of prefabricated bridge members depends on the strength of the concrete, the diameter of the steel bar, and the anchorage length. Furthermore, it is concluded that the mechanical bond strength accounts for 88% of the bond strength within prefabricated concrete.

Effect of silica-fume content on performance of CaCO3 whisker and basalt fiber at matrix interface in cement-based composites

The bond at fiber–matrix interface is considered as one of the most important factors influencing the performance of fiber reinforced cementitious composites (FRCC). To improve such bond, adding silica fume is considered as an effective and efficient method. In modern FRCC, CaCO3 (calcium carbonate) whisker and basalt fibers witnessed increasing popularity due to their effectiveness in improving mechanical performance at multi-scales. However, systematic research still lacks for the bond improvement at their fiber–matrix interface. In this regard, silica fume of various contents was added to plain concrete (PC), CaCO3 whisker reinforced cementitious composites (CWRCC) and basalt fiber reinforced cementitious composites (BFRC). The bond strength at the fiber–matrix interface and mechanical properties of PC, CWRCC and BFRC were evaluated. Test results show that the addition of silica-fume up to 10% could enhance the interface bond and mechanical properties of CWRCC and BFRC up to 30% and 34%, respectively. SEM analysis revealed improved bond at the fiber–matrix interface with addition of silica fume as evidenced by the fact that the whisker after pulled out from the matrix was encapsulated by cement paste, as compared to that of plain composite without silica fume. Moreover, EDS energy spectrum of whisker and basalt fiber surface show that the Si content increased noticeably as a result of the increased hydration products adhering to the whisker and basalt fiber surface, thus improving the bond at the fiber–matrix interface. The incorporation of silica-fume in BFRC lead to a large number of attached hydration products to the surface of fiber after pulling out. At the initial stage of cement hydration, dispersed silica-fume particles play a role of “crystal nucleus”, which can absorb Ca + and OH– ions, and increase the number of CH nuclei. Furthermore, silica-fume continuously reacts with CH and procedure C-S-H gel which decreases the porosity of the interface layer, makes the structure more compact and improves the interfacial adhesion. The microstructure of the interface layer is enhanced by C-S-H which is generated by “secondary reaction” and increase the interfacial bond strength of fiber and matrix. Lastly, a microstructure schematic representation for the fiber–matrix interface was developed to understand the mechanism between the fiber and the cement matrix.

Bond durability of BFRP bars embedded in concrete with fly ash in aggressive environments

Fiber-reinforced polymer (FRP) bars are an environmentally friendly alternative to steel and are considered ideal substitutes for steel reinforcement in marine concrete structures due to their excellent resistance to chloride ions and mechanical properties. However, the strong alkaline environment in concrete results in the degradation of FRP bars, and the degradation of FRP bars is detrimental to the long-term performance of these structures due to the decrease in interfacial bonding. This study aims to investigate the bond durability of basalt FRP (BFRP) bar and concrete with or without fly ash in corrosion environments by pull-out tests. The laboratory-accelerated aging environments are an alkaline solution (pH 12.8 ± 0.2) and simulated seawater, and the immersion temperatures are set at room temperature (~26 °C), 40 °C, and 60 °C. Furthermore, the mechanical properties of the BFRP bars are also determined under the same conditions. Results indicate that the mechanical properties of the BFRP bars and the bond strength decrease as the immersion time increases. The addition of fly ash in concrete can improve the interfacial bond strength. For instance, the bond strength of BFRP-ordinary concrete decreases by 69.0% when immersed in a 60 °C alkaline solution for 6 months, and that of BFRP-fly ash concrete decreases by 58.1% in the same immersion environment. The similar experimental phenomenon can also be obtained in seawater, which can be attributed to fly ash refining the concrete pores and inhibiting the reaction of alkaline with silica contained in the basalt fibers. Finally, the retention of bond strength is predicted based on the apparent horizontal shear strength of the BFRP.

Benefits of chemically treated steel fibers on enhancing the interfacial bond strength from ultra-high-performance concrete

This study investigated the effects of various chemical treatments on the pullout behavior of steel fibers in ultra-high-performance concrete (UHPC). Various methods used in previous studies were adopted and reproduced using macro straight steel fibers. The methods included acetone and acid washing, zinc phosphating, nanosilica coating, and ethylenediaminetetraacetic acid (EDTA) electrolyte solution treatment. The surface conditions and roughness of each treated fiber were analyzed using scanning electron microscopy and atomic force microscopy. The fiber pullout test results indicated that the surface roughness increased between 1.5 and 24.9 times, and that a roughened fiber surface leads to an improvement in the average bond strength. Acetone washing was the most effective in improving the pullout resistance of the fiber due to its cleansing effect. Acid washing resulted in a slip-hardening behavior, which improved the pullout energy significantly. The zinc phosphating treatment exhibited the lowest average bond strength increase rate. Nanosilica coating was found to considerably improve adhesion; however, it caused fractures as inclined. EDTA electrolyte solution treatment significantly improved the average bond strength in proportion to the surface roughness. By considering the energy absorption capacity, the optimum treatment time of EDTA electrolyte solution was proposed to be less than 6 h.

Effect of Argon Plasma on the Shear Bond Strength of Y-TZP Zirconia Ceramic Resin Interface

This study aimed to evaluate zirconia surface energy and shear bond strength after application of different argon plasma irradiation time. The zirconia blocks are divided into four groups. The surface of the specimens was coated by argon plasma with different irradiation times (2.5–15–20 min). The contact angles of specimens were measured with formamide to quantify surface hydrophobicity. Experimental groups were divided into two subgroups; in the first subgroups specimens were cemented with using ceramic primer and the second subgroups were cemented with resin cement without primer. After cementation, the shear bond strength test was realized. Data were analyzed by one-way ANOVA and post-hoc Tukey tests. p < 0.05 value was considered statistically significant. The highest mean shear bond strength (SBS) values were recorded in the application of 20 min laser irradiation time (Group A1: 28.45 ± MPa and Group A2: 24.69 ± 5.08 MPa). In the application of primer plus to Ar-plasma, SBS of all groups showed increased values however, only Group B (15 min plasma duration) and Group C (2.5 min plasma duration) revealed statistically significant different higher values. Zirconia surface energy increased with argon plasma application. In this way, the bond strength between zirconia and cement is strengthened.

Shear and tensile bond strengths of autoclaved aerated concrete (AAC) masonry with different mortar mixtures and thicknesses

Autoclaved aerated concrete (AAC) blocks are commonly used for masonry walls. In order to understand the strength of AAC masonry, it is essential to assess the tensile and shear bond strengths of the AAC block-mortar interface for various mortar combinations. This research investigates the bond strength of AAC block mortar interface made up of a) polymer modified mortar (PMM) and b) ordinary cement sand mortar of 1:4 or 1:6 ratio with thickness of 10mm, 15mm or 20mm. A thin cement slurry coating was applied on the block surface before placing the cement sand mortar in the masonry. For all types of interface, shear bond strength of masonry was studied using a triplet test, while the tensile bond strength was determined through a cross-couplet test. Among the cement sand mortar used in this study, cement sand mortar of ratio 1:4 and thickness 15mm showed the maximum shear strength of 0.13MPa with the failure of blocks as the predominant failure while the PMM had shear bond strength of 0.12MPa with the failure of blocks as the predominant failure type. However, in case of the tensile bond strength testing, PMM showed the tensile bond strength of 0.19MPa, which was highest among all the test specimens used in this study. Considering both the tensile and shear bond strengths of the AAC masonry and based on the observed failure pattern, among all the combinations used in the experiment, either PMM or cement-sand mortar of ratio 1:4 and thickness of 15mm can be chosen for the AAC masonry.

Experimental Research on Interfacial Bonding Strength between Vertical Cast-In-Situ Joint and Precast Concrete Walls

In the monolithic precast concrete shear-wall structure, the bonding property of cast-in-situ joints to precast concrete walls is important to ensure the entire structural performance. Aiming to the vertical joint of precast concrete walls, an experimental study was carried out considering the factors including the strength of precast and joint concretes, as well as the interface processing and casting age of precast concrete. The micro-expansion self-compacting concrete was used for the cast-in-situ joints. The interfacial bonding strength between joint and precast concrete was measured by splitting tensile test. Results show that the interfacial bonding strength was benefited from the increasing strength of joint concrete and the spraying binder paste on the interface of precast concrete, and unbenefited from the overtime storage of precast concrete. The washed rough surface with exposed aggregates improved the interfacial bonding strength, which increased with the increasing roughness. Based on the test results, the limits of the strength grade of joint concrete and the roughness of washed rough surface are proposed to get the interfacial bonding strength equivalent to the tensile strength of precast concrete. Meanwhile, the spraying of binder paste on precast concrete is a good choice, the storage time of precast components is a better limit within 28 days.

Thermal performance of the solar reflective fluorocarbon coating and its effects on the mechanical behavior of the ballastless track

A novel solar reflective fluorocarbon coating was proposed to improve the performance of ballastless tracks of high-speed railways at high temperature. Firstly, experiments were carried out to investigate the influence of the solar reflective fluorocarbon coating on the temperature field of coated concrete structures. Secondly, a non-linear finite element model of the ballastless track incorporating the non-linear properties of concrete and a cohesive zone relationship of interfaces between track components was established, and the numerical model was verified by on-site monitoring results. Then, based on the experimentally measured temperature fields, the efficiency of the solar reflective fluorocarbon coating on reducing temperature deformation of the track was quantified by finite element analysis, and the combined action of initial track component defects and bond properties between track components on the mechanical behavior of the coated track was analyzed. Finally, the influence of thermal performance of different coatings on mechanical behavior of the track was systematically investigated. Results show that the solar reflective fluorocarbon coating can reduce the surface temperature and the temperature gradient of the coated track by 10% and 14% respectively. After applying the solar reflective fluorocarbon coating to the ballastless track, the maximum slab end arching displacement, the rise of slabs in the lateral direction, and the maximum longitudinal stress of the concrete joints can be reduced by 20%, 19%, and 13% respectively. The combined action of initial track component defects and the interfacial bond strength should be considered when studying the thermal deformation of the ballastless track. Slab end arching displacements are mainly influenced by the surface temperature of the slabs.

Enhancement of FDM ULTEM® 9085 bond strength via atmospheric plasma treatment

Abstract The present study investigates a process to improve the bond strength of ULTEM® 9085 manufactured via fused deposition modeling and presents an application of this technique as a repair method for damaged 3D-printed structures. The initial surface characteristics, roughness, and wettability of AM parts are shown to vary with the print orientation. Atmospheric plasma treatment (APT) was utilized to improve the wetting characteristics and bond behavior of ULTEM® 9085 as verified by contact angle measurements, XPS analysis, and flatwise tensile testing. The plasma treated samples displayed improved wettability of the polymer surface with a decrease in the contact angle from 115° to 22°. Furthermore, flatwise tensile testing of treated samples that were initially hydrophobic showed a 35 % increase in interfacial strength. The surface modifications were characterized by XPS. Increases in the concentration of oxygen on the surface contributed to the improved wettability of the samples, while increases in the concentration of carboxyl groups led to enhanced interfacial bond strength with an epoxy paste adhesive. However, with overexposure to plasma treatment weakly bound ash forms on the surface and leads to a degradation of strength. An optimized plasma treatment is proposed for ULTEM® 9085, and an application for a repair doubler was tested. Utilizing a damaged tensile dogbone specimen, this plasma treatment and bonding technique are shown to produce a 100 % recovery of strength, demonstrating the applicability and potential for repairing 3D-printed structures.

Influence of silane type and application time on the bond strength to leucite reinforced ceramics

Introduction All-ceramic restorations currently dominate the market of indirect restorative materials due to their biocompatibility, longevity and superior aesthetics [1]. Silica-based ceramics, such as leucite, carry the advantage of being receptive to surface treatments, making them bondable to tooth substrates [2]. However, a standardised application protocol regarding silane coupling agents is lacking. Such step is critical to ensure durability of the restoration placed in situ. Post-etch cleaning and silane application have been proven to increase bond strength, however, this step varies for each material [3]. The aim of this research was to assess the influence of different types of silane coupling agents and respective application times on the bond strength of the ceramic-resin interface. Materials and methods Ten leucite reinforced glass ceramic blocks (IPS Empress CAD LT BL4/C 14) were divided into equal halves. Of the samples obtained, 6 were randomly divided into three groups according to the silane used: G1 BIS-Silane (Bisco, Schaumburg, IL, USA); G2 ESPE Sil Silane Coupling Agent (3 M ESPE AG, Seefeld, Germany); G3 Monobond Plus (Ivoclar-Vivadent, Schaan, Liechtenstein). Each was then divided into two subgroups, according to the surface conditioning time: T1 (1 min.) or T2 (5 min.). Each block was acid etched (HF 9.5% − 1 min), post-etching cleaned (OPA 37.5% − 1 min; ultrasonication − 2 min.) and silanized. Heat treatment was carried out at 100 °C (1 min.). Then a thin layer of Optibond FL (Kerr) adhesive was applied and each block was adhered to pre-heated resin at 55 °C. The samples were light cured for 40 s on each side (1200 mW/cm2). Samples were sectioned into microspecimens (1 ± 0.2 mm2) that were subjected to aging (10,000 thermocycles − 5 and 55 °C). The microspecimens were tested in tension at a crosshead speed of 0.5 mm/min, until they debonded. Data analysis was carried out by a two-way ANOVA, at a significance level of 5%. Results The group featuring BIS-Silane with longer application time (G1T2) presented a mean µTBS value (32.4 ± 19.6 MPa) significantly higher to all other groups (p < .001). Monobond Plus registered the lowest mean µTBS value (G3T1 − 18.5 ± 7.3 MPa) and (G3T2 − 17.3 ± 5.8 MPa). The type of silane coupling agent has shown to have a significant influence on the microtensile bond strength (p = .001; η 2=0.16). Discussion and conclusions Some authors have previously suggested that silanization could benefit from longer application times, but seldom research has been found featuring this variation protocol [3,4]. Silanes require a hydrolysation process in order to establish chemical bonds. Two-bottle systems show the highest bond strength results and may benefit from longer application times. The addition of 10-MDP seems to have no significant advantage over traditional silane coupling agents.

Microstructure and mechanical properties of Al/Mg/Al composite sheets containing trapezoidal shaped intermediate layer

In the present study, the Al 6061/Mg ZK60/Al 6061 composite sheets with the trapezoidal shaped intermediate layer were successfully obtained by multi-pass hot roll bonding. The microstructure and mechanical properties of the composite sheets under different rolling passes were investigated. The results demonstrated that the interface of the composite sheets achieved the strong interface metallurgy bonding, without discernible voids, cracks, and other defects. The introduction of the three-dimensional (3D) interface layer significantly improved the interface bond strength of the composite sheets. The interface layer composed of Al3Mg2 and Al12Mg17 was observed at the interface of the composite sheets. The thickness of the intermetallic compounds (IMCs) layer varied with the position of the interface, and the IMCs layer was the thinnest near the center of the sheet. The IMCs layer was continuously coarsening and fragmenting with the increase of rolling deformation, and stress concentration was easily generated at the interface between the Mg layer and the Al layer, so the crystal grains were more refined than that inside of the component sheets, which made the actual strength of the composite sheets higher than the theoretical strength. With the proceeding of the rolling process, the internal grain size of the component sheet gradually increased, and the interface products were coarsened and fragmented, which reduced the tensile properties of the composite sheets. The interface layer with moderate thickness and intact interface layer in the composite sheets appeared uniformly broken when it was under tensile stress, and the direction of microcracks generated was perpendicular to the tensile direction, which hindered the crack propagation and delayed the fracture of the composite materials and thereby enhanced the elongation of the composite sheets. Simultaneously, the trapezoidal shaped intermediate layer made the cracks deflect along the interface, which was conducive to the strengthening and toughening of the interface area, to improve the plasticity of the composite sheets.

Interfacial failure and arching of the CRTS II slab track reinforced by post-installed reinforcement bars due to thermal effects

To prevent damage of the China Railway Track System (CRTS) II slab track induced by thermal effects, post-installed reinforcement (PIR) bars between the prefabricated slabs and the concrete base have been utilized in the track. This work presents a study on the interfacial failure and arching of the CRTS II slab track reinforced by PIR bars due to the effects of temperature change. To this end, a novel finite element model of the track was established, in which the non-linear interfacial interaction between the track slabs and the cement asphalt (CA) mortar layer was simulated by a cohesive zone model, the non-linear constitutive material properties of track concrete were represented by a concrete damaged plasticity (CDP) model, and the non-linear bond-slip relationship between PIR bars and track concrete was characterized by non-linear spring elements. Comparison between simulation results and experimental data indicates that the proposed modelling technique is capable of evaluating the performance of the track reinforced by PIR bars. The combined action of insufficient bond strength between PIR bars and concrete, and insufficient bond strength between track slabs and CA mortar layer, was analyzed. Numerical analysis results show: (1) The temperature rise of interface failure between the concrete slabs and the CA mortar layer can be improved by 6 °C after PIR bars installation. (2) The PIR bars are effective in reducing arching displacement of slabs caused by temperature rise in both lateral direction and longitudinal direction of track slabs. (3) Both PIR bond strength and interface bond strength influence the maximum arching displacement of track slabs significantly.

Effects of different interface conditions on energy absorption characteristics of Al/carbon fiber reinforced polymer hybrid structures for multiple loading conditions

AbstractThe treatment of carbon fiber reinforced polymer (CFRP)–metal bond interface is very important for the practical application of CFRP‐reinforced metal structures in automobile, aviation, and other transportation vehicles. In this article, the effects of different interface connection conditions on the failure mode and energy absorption of hybrid tubes were studied by experimental and simulation methods. For this purpose, the two aspects metal surface treatment (sandblasting) and connection mode (socket, co‐curing, and secondary bonding) were used for adhesive joining. By observing the force–displacement curve, the energy absorption capacity of the hybrid tube under different interface connection conditions was quantified, and the performance was evaluated. The calculation results show that the interfacial connection conditions have different effects on the crashworthiness of the hybrid tube under different loading conditions. Among them, for axial crushing and transverse bending loads, the energy absorption characteristics of the hybrid tube can be effectively improved by sandblasting and cementing. Under the action of radial compression, although the roughness of the interface is increased by sandblasting, the energy absorption capacity is reduced rather than enhanced. In order to reveal the mechanism and make parameterized definitions of the interface characteristics, so as to effectively predict the finite element model is especially necessary. With the improvement of interface bond strength, its bearing limit distribution area also increases, and the corresponding deformation is also large, which eventually leads to more energy absorption under axial crushing and transverse bending loads. The increase in the interface connection strength has little effect on its crashworthiness under radial pressure.

Touch-Cure Polymerization at the Composite Cement-Dentin Interface

Ceramic restorations are often adhesively luted onto the tooth prep. The so-called touch-cure concept was developed to yield optimum polymerization of composite cement at the restoration-cement-tooth interface for immediate bond stabilization. Although this touch cure is theorized to initiate polymerization at the interface when the accelerator in the primer makes contact with the cement, this process has not yet been proven. This study aimed to elucidate the mechanism of touch cure by measuring the degree of conversion (DC) of composite cement applied with or without an accelerator-containing tooth primer (TP) versus an accelerator-free primer using real-time Fourier-transform infrared spectroscopy (RT-FTIR) and attenuated total reflection (ATR)–FTIR. Interfacial bond strength was measured in shear mode, the accelerator composition confirmed by X-ray fluorescence analysis (XRF), and the interfacial interaction of TP and composite cement with dentin investigated by X-ray diffraction (XRD), focused-ion-beam scanning electron microscopy (FIB-SEM) with 3-dimensional interface reconstruction, and transmission electron microscopy (TEM). RT/ATR-FTIR revealed the significantly highest DC when the composite cement was applied with the accelerator-containing primer. XRF disclosed a vanadium compound as a novel chemical accelerator within TP, instead of a classic chemical curing initiator system, to set off touch cure as soon the cement contacts the previously applied primer. Although the TP contains the acidic functional monomer 10-MDP for adhesion to tooth tissue, touch cure using the accelerator-containing TP combined the fastest/highest DC with the highest bond strength. FIB-SEM and TEM confirmed the tight interfacial interaction at dentin with submicron hybridization along with stable 10-MDP also Ca-salt nanolayering.

Effects of different surface treatments and adhesive self-etch functional monomers on the repair of bulk fill composites: A randomised controlled study

ObjectiveTo evaluate the effect of different adhesive protocols on the microtensile bond strength (μTBS) and integrity of the repaired bulk fill composite interface. MethodsTwo hundred and seventy composite blocks made of bulk fill composites of different viscosity were randomly assigned to 18 surface conditioning groups (n = 15/group). The universal adhesive systems used were Heliobond™, Tokuyama bond force II™ and Scotchbond Universal™. A nanohybrid resin composite was applied as the repair material. Negative and positive control groups were included. Stick shape specimens of each group were subjected to μTBS testing. Representative samples from all test groups were subjected to microscopic, profilometric and SEM examination to determine their mode of failure. The data were analysed statistically using two-way ANOVA test, Tukey’s test and the independent t-test (α = 0.05). ResultsThe mean μTBS of all test groups ranged between 28.5 and 46.8 MPa and varied with the type of adhesive system employed. Significantly highest μTBS values were obtained when Tokuyama bond force II™ and Scotchbond Universal™ adhesives were used (p < 0.01) which were comparable to the coherent strength of the bulk fill resin composite in the positive control groups (p > 0.05). The viscosity of the bulk fill composite did not significantly influence repair bond strength. The microscopy and SEM examination of the failed interfaces revealed a mixture of adhesive and cohesive failures. ConclusionsUnder the tested conditions, significantly greater μTBS of repaired bulk fill composite was achieved when the substrate surface was treated with adhesive systems containing a functional monomer. Clinical significanceEff ;ecting a repair of a bulk fill resin composite restoration with the application of a functional monomer containing adhesive system, such as Tokuyama Bond Force II™ or Scotchbond Universal™, would seem to enhance the interfacial bond strength and integrity of the repaired resin composite interface.

Spindle-Shaped Surface Microstructure Inspired by Directional Water Collection Biosystems to Enhance Interfacial Wetting and Bonding Strength.

Unique spindle microstructures with an apex angle of ∼20° bring the ability of directional water collection to various biosystems (i.e., spider silk and cactus stem). This has great potential to solve the insufficient interfacial wetting for mechanical interlocking formation between polymers and substrates. In this study, the bioinspired spindle microstructures were easily fabricated through the deposition of molten materials by a nanosecond laser with an overlap ratio of 21% between laser spots and achieved superior interfacial wetting for commercial epoxy adhesive on aluminum substrates. Detailed analyses show that there are four mechanisms responsible for the superior interfacial wettability of bioinspired spindle microstructures: the Laplace pressure difference, newly formed aluminum oxide, the capillary effect, and no extra pressure from a trapped atmosphere. Consequently, the bioinspired spindle surface microstructures achieve a maximum improvement of ∼16 and ∼39% in interfacial bonding strength before and after water soak exposure compared to the as-received condition. Moreover, the stable interfacial wettability of bioinspired spindle microstructures ensures that the improved joint strength varied little with an increase in surface roughness from ∼1.7 to ∼12.8 μm. However, the interfacial wettability of common dimple microstructures deteriorated with an increase in surface roughness, which is indicated by the decreasing rule in the quadratic polynomial function of the interfacial bonding strength as the surface roughness increases from ∼2.1 to ∼18.2 μm.

Experimental study on the interfacial bond strength and energy dissipation capacity of steel and steel fibre reinforced concrete (SSFRC) structures

In this study, to address the problems faced while constructing steel reinforced concrete (SRC) structures, such as the positional conflicts between the shaped steel and steel bars or the difficulty in pouring concrete, we propose a novel ‘Steel and Steel Fibre Reinforced Concrete’ (SSFRC) composite structure, wherein the steel reinforcement cage in SRC is replaced with steel fibres. We designed 20 square-section specimens and performed push-out tests to evaluate the bond properties between the shaped steel and steel fibre reinforced concrete experimentally. The influence of the steel fibre volume rate (ρsf), length-to-diameter ratio (Le/D0), and thickness of concrete cover (Css) on the interfacial bond strength, energy dissipation capacity, and interfacial damage were investigated. In addition, the ultimate bond strengths of SSFRC and SRC were compared. The results indicate that the novel SSFRC composite structure increases the ease of construction and has an ultimate bond strength that is similar to that of SRC. The interfacial energy dissipation increases with the increase in Le/D0, ρsf, and Css, and the steel fibres slow down the development of damage in the concrete specimens. Based on the results, we present an economical and effective method for determining the critical thickness of the concrete cover for SSFRC members. The thicker the concrete cover, the slower the interfacial damage development during the later stages of the test.