Bond Strength Research Articles

Effects of laser treatment on bond strength of epoxy resin and calcium silicate-based sealers: a systematic review and meta-analysis of in vitro studies.

This study aimed to systematically review the effect of laser treatment on the bond strength of epoxy resin-based and calcium silicate-based endodontic sealers to root dentine. The search encompassed four databases: PubMed/MEDLINE, EMBASE, Scopus, and ISI Web of Science. Inclusion criteria were limited to in vitro studies conducted on extracted human teeth evaluating bond strength in megapascals (MPa) of either epoxy resin-based or calcium silicate-based sealers, using the push-out test. Two independent reviewers appraised the methodological quality of the selected studies to assess the risk of bias. Meta-analysis was performed for different laser types, endodontic sealers, and control groups. Standard Mean Difference and 95% Confidence Interval values were calculated. 17 studies met the inclusion criteria for qualitative synthesis, and 15 for quantitative analysis. Meta-analyses revealed that certain lasers (Er,Cr:YSGG, Er:YAG) significantly increased bond strength for epoxy resin-based sealers when compared to negative controls (inert solutions), but did not show a significant advantage over EDTA agent. For calcium silicate-based sealers, laser treatment did not show significant enhancement in bond strength compared to either inert solutions or EDTA. The subgroup analysis suggested that erbium lasers, especially in the PIPS mode, potentially increase the bond strength of epoxy resin-based sealers. Laser treatment enhances the bond strength of epoxy resin-based sealers compared to inert solutions, but not more than EDTA. For calcium silicate-based sealers, laser treatment does not significantly improve bond strength over inert solutions or EDTA. Laser treatment increases the bond strength of epoxy resin-based sealers.

C(sp3)−F Bond Activation by Lewis Base‐Boryl Radicals via Concerted Electron‐Fluoride Transfer

AbstractSelective C−F bond activation through a radical pathway in the presence of multiple C−H bonds remains a formidable challenge, owing to the extraordinarily strong bond strength of the C−F bond. By the aid of density functional theory calculations, we disclose an innovative concerted electron‐fluoride transfer mechanism, harnessing the unique reactivity of Lewis base‐boryl radicals to selectively activate the resilient C−F bonds in fluoroalkanes. This enables the direct abstraction of a fluorine atom and subsequent generation of an alkyl radical, thus expanding the boundaries of halogen atom transfer reactions.

Anatase‐reinforced PtZn@Silicalite‐1 structured catalysts boosting propane dehydrogenation

AbstractStructured catalysts exhibit the advantages of high diffusion efficiency and low heat transfer resistance, which have attracted increasing attention to non‐adiabatic gas–solid process. However, the metal‐supported coating catalysts face the problems of weaker bond strength and severe sintering, especially under the conditions of large flow rate and high temperature. Herein, metal@Silicalite‐1 structured catalysts with high adhesion and thermal stability were successfully prepared by hydroxylating the substrate with anatase. Rich surface Ti‐OH significantly strengthened the adhesion stability of the zeolite coating. In propane dehydrogenation reaction, the optimized PtZn@S‐1‐15Ti showed a high specific activity of 49.6 molC3H6·molPt−1·s−1 with propylene selectivity above 99% at 600°C. The introduction of anatase accelerated the aggregation of silicon sources and induced nucleation with growth content of zeolite increased by 3.6 times. It breaks the inherent contradiction between high loading amount and strong binding ability of coated catalysts, which broadens the avenues for industrial applications.

Modulating Electronic Structure of MoS2 nanosheets by Sulfide‐Enrichment‐Induced Vacancies for Enhanced Photocatalytic Hydrogen Production

Enhancing photocatalytic activity by changing the electronic structure of the catalyst is an effective strategy. 2H‐MoS2 has semiconductor properties, and its unsaturated side S atom is the main active site for its photocatalytic activity. However, due to the weak S‐H bond energy, its hydrogen adsorption capacity is weak. In this work, the electronic structure of MoS2 is adjusted by S‐rich treatment, resulting in the formation of Mo vacancy (MoS2‐VMo). The level of Mo vacancies was assessed using UV‐visible diffuse reflectance spectroscopy (UV‐vis DRS). As these vacancies can capture certain photogenerated electrons, thereby reducing the recombination of electron‐hole pairs. Through DFT calculation, it is found that the anti‐bonding orbital electron filling of MoS2‐VMo is weakened, the bond energy of S‐Mo bond is weakened, and the bond energy between S‐H bond is enhanced, which is more conducive to proton adsorption. The photocatalytic activity for hydrogen evolution of MoS2‐3, which underwent the optimal S‐rich treatment, achieved a remarkable rate of 2404.6 μmol g‐1 h‐1 in dye eosin Y (EY) sensitization system, significantly surpassing that of MoS2 lacking the S‐enriched treatment. This study introduces a novel concept for enhancing the photocatalytic hydrogen evolution performance of metal sulfides via defect engineering.

Provides Efficient Shear Bond Strength and Durability Between Lithium Disilicate Glass-ceramic and Resin Cement: A Potential Alternative to the Conventional Hydrofluoric Acid Protocal

Objectives: This study investigated the effects of two surface treatment protocols on the shear bond strength, bond durability, and failure mode at the interface between lithium disilicate glass-ceramic and resin cement. The protocols compared were a self-etching ceramic primer and the conventional hydrofluoric acid (HF) etching followed by silane. Methods: Fifty lithium disilicate specimens were randomly divided into five surface treatment groups (n=10 each). A control group received no treatment. The remaining 4groups included: 5% HF etch with Monobond Plus thermocycled and non-thermocycled, Monobond Etch & Prime (MEP), thermocycled and non-thermocycled. Microshear bond strength (microSBS) was assessed before and after thermocycling to evaluate bond durability. Failure modes (adhesive, mixed, cohesive in resin/ceramic) were recorded under a stereomicroscope. Results: Both surface treatment protocols exhibited comparable microSBS for both pre- and post-thermocycling results. Moreover, bone durability obtained from the two treatment protocols seemed to be comparable. Most groups displayed adhesive/mixed failures. Notably, the self-etching ceramic primer group showed cohesive failure in half of the specimens initially, persisting in 20% after thermal aging. Conclusions: Compared with the conventional HF protocol, the self-etching ceramic primer protocol provided similar microSBS and bond durability between lithium disilicate glass-ceramic and resin cement. The data suggest a self-etching ceramic primer is a viable option for the conventional HF protocol in bonding to glass-ceramic, minimizing the HF hazard and simplifying the clinical procedure.

Reversible Demountable Coating Films Composed of Trifunctional Liquid Anthracene Compounds and Evaluation of Their Adhesive Properties

AbstractTechnologies that facilitate recycling are attracting considerable interest from the perspective of resource constraints. In the present study, degradable primer films are to facilitate the removal of strongly bonded joints. This film consists of a light‐cured trifunctional anthracene compound that thermally decomposes to its original liquid state. To demonstrate its function as a degradable primer film and verify its range of applications, various substrates, such as aluminum alloys, stainless steel, carbon fiber‐reinforced plastics, carbon fiber‐reinforced thermoplastics, and polyetheretherketone, are bonded through the primer film using a two‐component epoxy adhesive. All the single‐lap specimens exhibit strengths above 10 MPa, which is sufficient, or base material fracture. When adhesive bonding specimens prepared using the same procedure are heated at 180 °C to transform the coating film to a liquid state, the bond strength is significantly reduced. The primer film is expected to exhibit long‐term stability of more than one year at ≈60 °C.

Electronic asymmetry of lattice oxygen sites in ZnO promotes the photocatalytic oxidative coupling of methane.

Photocatalytic oxidative coupling of methane with oxygen is promising to obtain valuable muti-carbon products, yet suffering low reactivity. Here, we apply cerium modifications on zinc oxide-supported gold catalysts based on the electronic asymmetry design of lattice oxygen to improve the coupling activity. The methane conversion rate exceeds 16000 μmol g-1 h-1 with muti-carbon selectivity of 94.9% and catalytic durability of 3 days, and it can increase to 34000 μmol g-1 h-1 under more thermal assistance, with a turnover frequency of 507 h-1 for ethane and an apparent quantum efficiency of 33.7% at 350 nm. According to systematic characterizations and theoretical analysis, cerium dopants not only can boost the formation of reactive oxygen species but also intervene in the vivacity of lattice oxygen by manipulating metal-oxygen bond strength, thereby leading to favorable methyl desorption to form ethane and quick water release. This work provides insight into the rational design of efficient photocatalysts for aerobic methane-to-ethane conversion.

Sulfate Oxyanion Steered d-Orbital Electronic State of Nickel-Iron Nanoalloy for Boosting Electrocatalytic Performance.

Oxyanion groups recently offer an innovative avenue for improving the sluggish kinetics of electrochemical reactions benefitting from their particular polyanion configurations and large electronegativity. Nevertheless, the exact structure design and deep regulating mechanism of oxyanion species remain poorly understood. Herein, a fresh architecture of the sulfate oxyanion coordinated nickel-iron nanoalloy on nitrogen and sulfur co-doped carbon nanotube (SO4 2--NiFe/NSCT) is newly proposed to study the activity increment effect and mechanism. The SO4 2--NiFe/NSCT displays hierarchical nanostructure with robust-wrinkled surface and highly efficient active sites. Importantly, the SO4 2- group, as a significant manipulation factor, is first evidenced to promote the oxygen reduction reaction (ORR) activity for NiFe nanoalloy under the reductive condition, showcasing outstanding bifunctional properties toward ORR and oxygen evolution reaction (OER), as well as the exceptional performance in non-aqueous Li-O2 battery. Both experimental and theoretical results elucidate that, as an electron bridge, the introduction of SO4 2- downshifts the d-band center of SO4 2--NiFe/NSCT and gives the electron transfer passageway between the H atom in OH* intermediate and the O atom in SO4 2- group, greatly optimizing the metal-intermediate interaction with weaker bond energy. This work provides a deep insight into the activity enhancement mechanism by the sulfate oxyanion.

Effect of Post Sizes and Citric Acid Treatment on the Bond Strength of Fiber Posts Using Self-Etch Resin Cement in Calcium Silicate–Based Sealer Treated Teeth

Abstract Objectives This study evaluated the effects of different post sizes and citric acid (CA) treatment on the bond strength of fiber posts cemented with self-etch resin cement in teeth obturated with calcium silicate–based sealer. Materials and Methods Seventy mandibular premolars were collected and randomly distributed to either a control group (no sealer) or experimental groups obturated with calcium silicate–based sealer (iRoot SP). The experimental groups were classified by post sizes—1.25 mm (no. 1), 1.375 mm (no. 2), and 1.50 mm (no. 3)—and the irrigants used (distilled water [DW] or CA). Prefabricated fiber posts were fixed using NX3 self-etch resin cement. Push-out bond strength was tested in the coronal and middle sections of the roots. Statistical Analysis The data were analyzed using a one-way analysis of variance (ANOVA), followed by a post hoc Duncan test. Results In the coronal section, post size no. 1 with DW showed significantly lower bond strength compared to the other experimental groups (p < 0.05). In the middle section, the larger post sizes (nos. 2 and 3) with CA treatment resulted in a significant increase in bond strength compared to the control group (p < 0.05). Conclusions iRoot SP negatively affected bond strength in the middle section of the canal. However, using larger post sizes (nos. 2 and 3) with CA treatment improved bond strength in the middle section.

Improvements to the bonding condition of ultra-thin concrete overlays for airport rigid pavements

ABSTRACT Ultra-thin concrete overlay (UTO) is an effective solution for repairing functional deficiencies in airport rigid pavements, with interface bonding properties critical to pavement performance and longevity. This study systematically investigates methods to enhance UTO interface bond strength under heavy dynamic loads. Aircraft dynamic simulations were performed to analyze stress states during landing, taxiing, and turning, identifying the required ultimate bond strength to prevent interface failure. Laboratory tests measured the shear and pull-out strengths of new and old concrete interfaces. A styrene–butadiene rubber (SBR) modified cement quartz mortar adhesive was developed with optimal curing conditions, and the effects of grooving intervals on bonding strength were assessed. Results demonstrated that the interface treatment increased the safety factor for tensile failure from 0.69 to 1.25 and for shear resistance from 0.61 to 1.12 under dynamic loads. This research provides a scientific basis for enhancing UTO applications in the functional rehabilitation of airport rigid pavements, offering a practical solution to improve safety and durability in high-stress environments.

Performance Research and Engineering Application of Fiber-Reinforced Lightweight Aggregate Concrete

Low strength and low impact toughness are two of the main issues affecting the use of lightweight aggregate concrete in harsh cold environments. In this study, the strength of concrete was improved by adding high-strength fibers to bear tensile stress and organize crack propagation. Four sets of comparative experiments were designed with freeze–thaw cycles of 0, 50, 100, and 150 to study the mechanical properties of fiber-reinforced lightweight aggregate concrete under freeze–thaw conditions. A detailed study was conducted on the effects of freeze–thaw on the compressive strength, flexural strength, impact toughness, and microstructure of concrete with different fiber contents (3, 6, and 9 kg/m3). The results show that for ordinary lightweight aggregate concrete, under the freeze–thaw cycle, the internal pore water of the concrete froze and generated expansion stress, resulting in tensile cracks inside the concrete. The cracks gradually accumulated and expanded, ultimately leading to cracking and damage of concrete structures. After 150 cycles, the strength loss rate exceeded 25%. When adding a reasonable amount of fiber (6 kg/m3), the fiber took on the tensile stress and hindered the development of internal cracks, significantly enhancing the splitting tensile strength, flexural strength, and impact toughness of lightweight aggregate concrete. And the failure pattern of concrete was significantly improved. At the beginning of the freeze–thaw cycle, the internal tensile stress was less than the fiber tensile strength and the fiber–matrix bonding strength, and the strength reduction rate of the concrete was slow. Relying on the friction absorption capacity between the fiber and the matrix, the fiber used its own deformation to resist the tensile stress. In the late stage of the freeze–thaw cycle, due to the destruction of the fiber–matrix transition zone structure, the bond strength decreased, the crack resistance and toughening effect decreased, and the strength of the concrete decreased rapidly. Moreover, the reduction in impact toughness was greater than the compressive strength and flexural strength under static load.

Current Evidence and Advances in CAD-CAM Resin Composite Blocks for Chairside Dental Restorations: Where Are We Now? A Scoping Review

Objective: This study aimed to determine the status of the scientific literature on CAD-CAM resin blocks by mapping the available evidence and identifying knowledge gaps. Data/Source: A systematic search of studies investigating CAD-CAM resin blocks was conducted. Risk of bias was assessed, and data on study designs, level of evidence, compositional classification, manufacturer, commercial brand, and properties investigated were extracted. This review followed Arksey and O’Malley’s five-stage framework and utilized Medline (OVID), EMBASE, and Scopus (Elsevier) databases. Study Selection: Study selection resulted in 27 studies for data extraction out of 209 studies screened from an initial pool of 529 studies. High sampling bias related to sample size and randomization was observed in almost all studies. Most studies (99%) were conducted in vitro, with low levels of evidence. The most common composition was “nano-ceramic”. 3M ESPE was the manufacturer with the most investigated blocks, and their product, 3M™ Lava™ Ultimate Restorative, was predominant in the selected investigations. Methodological heterogeneity was extensive among the studies, with mechanical properties (38%) and bond strength (35%) being the most commonly investigated outcomes. Conclusion: This scoping review indicates an increasing trend in dental research assessing CAD-CAM resin blocks. However, the overall level of evidence derived from these studies is low, predominantly consisting of in vitro investigations. Clinical Significance: The findings underscore the need for clinical trials to augment the level of evidence and enable long-term assessment of CAD-CAM resin blocks. Dentists should be cautious while interpreting the findings from in vitro studies, as the outcomes may not directly translate to clinical success.

Comparison of the effects of laser systems and cold atmospheric plasma on the surface roughness and shear bond strength of flexible hybrid ceramics.

The aim of this study was to compare the effects of laser systems and cold atmospheric plasma (CAP) on the surface roughness (Ra) and shear bond strength (SBS) of flexible hybrid ceramics (FHCs). Eighty FHC samples were divided into 5 groups to be subjected to surface treatments (hydrofluoric acid (HFA), HFA + 5W Er: YAG laser (HFA + 5WE), HFA + 3W Er: YAG laser (HFA + 3WE), HFA + ultrafast fiber laser (HFA + FL), and CAP). The Er: YAG laser (AT Fidelis Plus III, Fotona, Slovenia) was operated with a 0.9mm diameter tip, delivering 250mJ and 150mJ per pulse, with output powers of 5W and 3W, and fluences of 23,623J/cm² and 14,157J/cm², respectively, at a frequency of 20Hz and a pulse duration of 600 µs for 30s. The FL (FiberLAST Inc., Turkey) was applied with a 7mm spot size, 1mJ pulse energy, 20W output power, 100kHz repetition rate, ultrashort pulse length (100 ns), and the fluence of 1,820J/cm² for 7s. The CAP (PiezoBrush PZ3, Relyon Plasma, Germany) applied to the surfaces for 80s at a treatment speed of 5 cm2/s and 100% plasma power. After the Ra values were measured, each group was divided into 2 subgroups to be cemented with total-etch (TE) and self-adhesive (SA) resin cements. The SBS of all the samples was measured. One sample was randomly selected from each group, and the fractured surfaces were examined by SEM analysis. The significance level was at P < 0.05. HFA + FL had the highest Ra values, and there was no significant difference between HFA + FL and HFA + 5WE (P > 0.05). There was no difference in Ra between CAP and HFA (P > 0.05). The highest SBS values were observed for the samples cemented with TE after HFA + FL. The difference between the SBS values of the groups cemented with TE after CAP, HFA + 5WE, HFA + 3WE, and HFA + FL was not significant (P < 0.05). The use of FL may be a promising method to improve SBS without causing thermal damage when using TE or SA cements. CAP can be recommended as a practical and safe treatment with SA cement because it is suitable for chairside use with a handheld device and does not change the physical properties of the material.

Redispersible Acrylic Ester Polymers: Effect of Polymer Property Changes Due to Polymerization Method Modification and Functional Additives on the Performance of Polymer Cement Mortar

This paper presents an experimental study aimed at improving the performance of polymer cement mortar by evaluating the properties of acrylic ester redispersible polymers, synthesized using a change in polymerization method from emulsion monomer to monomer dropwise addition methods, along with the use of a functional additive in the form of a foaming agent. To achieve the research objectives, a polymer with a glass transition temperature of −11 °C was synthesized by fixing the monomer ratio, particle-size distribution, and glass transition temperature, and the physical properties of the polymer cement mortar were assessed. The results showed that polymers synthesized using the modified polymerization method increased elongation at break and possessed a 35% smaller average particle size. The use of the foaming agent also resulted in enhanced tensile strength. The polymer cement mortars made with these respective polymers demonstrated improvements in compressive strength 11~25%, flexural strength 53~77%, bond strength 78~113%, volumetric changes 65~88%, and water absorption 30~70%. These findings suggest that changes in the polymerization method and the incorporation of functional additives influence the average particle size and air entrainment control properties of the polymers, thereby positively impacting the performance of the cement hydrates.

Polyvinyl Butyral Solid Electrolyte Film and Its Electrochromic Laminated Safety Glass.

In recent years, the application of electrochromic laminated safety glass has attracted more and more attention, relying on polyvinyl butyral (PVB) solid electrolyte film. Herein, the ionic conductivity (σ) of the PVB film has been improved by a cross-linked structure and blended with LiClO4, which can reach as high as 1.78 × 10-4 S cm-1 at room temperature. In addition, their excellent comprehensive characteristics have been confirmed, such as mechanical strength, high visible light transmittance (>90%), high bond strength (4.2 MPa), and excellent thermal stability. Based on the PVB film above, WO3-laminated electrochromic devices with 5 × 5 cm2 and 10 × 10 cm2 areas are constructed. They can remain stable after 20 000 cycles monitored by cyclic voltammetry curves, indicating the PVB solid polymer electrolyte (PSPE) with a cross-linked structure has the potential commercial viability of large-area electrochromic devices (ECDs).

Effects of primer components of silane and 10-methacryloyloxydecyl dihydrogen phosphate on resin bonding to tribochemical silica-coated highly translucent zirconia.

To assess the influence of different primer compositions-silane (S), 10-methacryloyloxydecyl dihydrogen phosphate (MDP), and the combination of silane and MDP (S + MDP)-on the bonding performance of MDP-free and MDP-containing resin cements to highly translucent zirconia. Tribochemical silica-coated zirconia plates were pretreated with one of three experimental primers, S, MDP, or S + MDP, with untreated specimens serving as controls. Subsequently, these plates were bonded to stainless-steel rods using either two MDP-free or two MDP-containing resin cements. Tensile bond strength was measured after 24h (TC0) and following thermal cycling (4-60°C for 10,000 cycles; TC10,000). Data were analyzed using a three-way analysis of variance (ANOVA), followed by one-way ANOVA and Tukey-Kramer post hoc tests (α = 0.05). X-ray photoelectron spectroscopy (XPS) assessed the elemental mass concentrations on the zirconia surfaces. For MDP-free resin cements, MDP-treated specimens exhibited significantly greater bond strengths than controls, regardless of the aging conditions. However, a significant reduction in bond strength was observed between TC0 and TC10,000 in most of the MDP-free resin cement groups, except for one S + MDP group. Conversely, for MDP-containing resin cements, the S + MDP group exhibited no statistically significant differences between aging conditions. Notably, XPS analysis detected silicon, zirconium, and aluminum on the zirconia surfaces. No significant difference in tensile bond strength was observed between aging conditions for MDP-containing resin cements bonded to tribochemical silica-coated zirconia primed with S + MDP. The combination of MDP-containing primers and resin cements demonstrated superior bonding performance to tribochemical silica-coated zirconia.

Surface Modification of Glass Fiber-Reinforced Composite Posts by Hydrogen Peroxide: A Scoping Review

AbstractOn the rehabilitation of endodontic treated teeth using intraradicular retention, adhesive failures often occur between the intraradicular post and the resin-matrix cement. The main aim of this study was to conduct a scoping review on the surface modification of glass fiber-reinforced composite posts by hydrogen peroxide solutions. An electronic search was performed in the PubMed database, using combinations of keywords pursuing articles published between 2010 and 2024 in English language. Of the 13 selected studies, 12 investigated the bond strength between the glass fiber-reinforced composite (GFRC) post and the resin-matrix cement after the surface treatment of the post, 5 articles analyzed failures using a stereomicroscope, and 7 studies analyzed the surface topography by scanning electron microscopy (SEM). Etching procedures with hydrogen peroxide (H2O2) altered the surface of the GFRC post by selectively dissolving the matrix without damaging the fibers, resulting in a larger surface area of exposed fibers available to react with the adhesive system or silane. Studies revealed high bond strength values between the etched GFRC posts to the resin-matrix materials. Surface treatment of GFRC posts with hydrogen peroxide seems promising considering the feasibility on the surface modification resulting in the improvement of bond strength of intraradicular posts to resin-matrix cements.

Conformation and Bonding of Lanthanide(III) Trihalides LnX3 (Ln = La-Lu; X = F, Cl, Br): A Relativistic Local Vibrational Mode Study.

This study employed relativistic methods to investigate the connection between the conformation and bonding properties of 45 lanthanide trihalides LnX3 (Ln: La-Lu; X:F, Cl, Br). Our findings reveal several insights. The proper symmetry exhibited by open-shell LnX3 requires the inclusion of spin-orbit coupling, achieved with 2-component relativistic Hamiltonians. Fluorines (LnF3) primarily exhibit pyramidal structures, while chlorides and bromides tend to yield planar conformations. For a given halide, the strength of Ln-X bonds increases across the lanthanide series, another outcome of the lanthanide contraction. Both strength and covalency of Ln-X bonds decrease upon the halide, i.e., LnF3 > LnCl3 > LnBr3. We introduced a novel parameter, the local force constant associated with the dihedral β(X-Ln-X-X), ka(β), which quantifies the resistance of these molecules to conformational changes. We observed a correlation between ka(β) and the covalency of the Ln-X bond, with higher ka(β) values indicating a stronger covalent character. Finally, the degree of pyramidalization in the LnX3 structures is connected to (i) the extent of charge donation within the molecule and (ii) the greater covalency of the Ln-X bond. These findings provide valuable insights into the interplay between the electronic structure and molecular geometry in LnX3.

Evaluation of Structural Transition Joints Cu-Al-AlMg3 Used in Galvanizer Hangers

The paper deals with the evaluation of the quality of Cu-Al-AlMg3 structural transition joints (STJ) made by explosion welding proposed for the renovation of galvanizer hangers. The three-layer joint consisted of electrolytic copper with a thickness of 25 mm, 2 mm of aluminium represented by the AW1050 alloy, and 25 mm of the EN AW 575 aluminium alloy. Light microscopy analysis confirmed the wavy pattern of both interfaces of the welded joint and significant plastic deformation in close proximity to the waves. Microhardness measurement revealed a partial strain hardening of the AW5754 copper-aluminium alloy near the interface and a significant increase in microhardness in the vortex zone of waves, reaching a value of up to 863 HV 0.025. Microcracks were also observed in these places. The intermetallic phase Al2Cu was identified in the vortex zones by XRD analysis. As a continuous layer of intermetallic phase was not observed in the interface of the welded joint, it is possible to consider the used welding parameters as appropriate. A semi-quantitative EDX analysis revealed a diversity of chemical composition in the vortex zones, which does not correspond to the phase composition based on the equilibrium binary Al-Cu diagram due to non-equilibrium conditions in the formation of the welded joint interface. The bond strength of three-layer welded joint evaluated by the strength test ranged from 151 to 171 MPa, which represented approximately a two-fold increase in comparison to the ultimate tensile strength of alloy AW1050, while the failure occurred in all samples at the AW1050-AW5754 alloy interface.

Bond of FRP bars in fine‐grained alkali‐activated concrete

AbstractAlkali‐activated cement (AAC) is an alternative binder with a promising potential to replace ordinary Portland cement (OPC) and mitigate its environmental issues. The use of fiber‐reinforced polymer (FRP) reinforcements with AAC concrete enables the development of corrosion‐resistant, environmentally friendly reinforced concrete structures. Bond behavior is critical in reinforced concrete structures and must be thoroughly studied for such new alternative materials. This study employs pullout tests to investigate the bond behavior between FRP bars and fine‐grained AAC concrete. Three fine‐grained AAC concretes with low to high strength, glass and carbon FRP bars and wrapped, milled, and smooth surface treatments were examined. The effect of bar casting position was also investigated. The compressive strength showed a significant influence on the bond strength. An average bond strength of approximately 18 MPa was observed for both glass and carbon FRP bars when used with 65 MPa concrete. Both the glass and carbon FRP bars with wrapping showed a lower bond strength than their milled FRP bars counterparts. The carbon bars without surface preparation (smooth bars) resulted in a much lower bond strength, around 4 MPa. In terms of casting positions, the bars cast in the middle section of the concrete block showed a higher bond strength than those at the bottom and top.