Papers by Keyword: Bond Strength

Abstract: The objective of this study was to analyse the variation of the average roughness (Ra) of a dental ceramic based on lithium disilicate after the etching of the surface with hydrofluoric acid (HF) in different concentrations in relation to the bond strength of this ceramic to the resin cement. The vitroceramic samples were divided into three groups: G1 (control, without etching), G2 (etching with HF 5%) and G3 (etching with HF 10%). The samples were exposed to the HF for 20 seconds at both concentrations. The average surface roughness after etching was analysed using the Confocal Zeiss Axio CSM 700 microscope and after the cementation and photoactivation of the resin cement the samples were submitted to a micro-shear test. The morphological analysis showed that the etching promoted the dissolution of the vitreous component and exposed the crystals of the ceramic for both concentrations, increasing the Ra values in relation to the control group (G1 = 0.331 ± 0.012 μm, G2 = 0.742 ± 0.126 μm; G3 = 1.335 ± 0.217 μm), with G3 having the highest Ra value. The highest values of bond strength were obtained by G3, with G1 = 17 ± 1.38 MPa, G2 = 24 ± 1.47 MPa and G3 = 30 ± 2.83 MPa. It can be concluded that the increase of the Ra by the HF etching promoted an increase of the bond strength between the lithium disilicate and the resin cement. However, the most effective superficial etching was with 10% HF.

Abstract: In tri-layered Cold Roll Bonded (CRB) composite sheets of dissimilar metals, uneven thickness reduction of the different layers have been observed. This has been explained by the difference in yield strength/flow stress of the metals. The aim of this research was to study if these observations also depend on different parameters such as stacking sequence and initial sheet thickness, as opposed to only material properties. Hence, tri-layered CRB composite sheets consisting of AA6082 and IF-steel were produced with two different stacking sequences, St/Al/St vs Al/St/Al. Two different layer thicknesses of the intermediate layer were used. Rolling was performed in a single pass achieving approximately 55-65% total thickness reduction. Comparisons between the samples are given, focusing on the reduction of thickness achieved in each layer, the roll bonded interface characteristics and the bond strength of the joints. The overall thickness reduction achieved in each layer was found to be similar for both metals in both stacking sequences for the considered material combination. The stacking sequence is statistically found not to have any effect on the bond strength of the joints. The thickness of the intermediate layer does not significantly affect the overall bond strength of the composite sheet for both stacking sequences. These findings are opposed to earlier results found in the literature.

Abstract: Epoxy coated reinforcements have been used extensively in bridge decks and substructures to protect against corrosion brought on by de-icing salts or marine environments. They need longer development lengths because of poor bond to concrete and special treatments on sites due to vulnerability of damage during transportation, storage and bending process. A new method of pre-heating of reinforcement before coating process using an IGBT(Insulated Gate Bipolar Transistor) control was applied to improve the bond of epoxy coating to reinforcements. In this paper, the bond-slip properties of newly developed epoxy coated bars are investigated and compared to those of black bars. The direct pull out test according to EN Standard was used with varying the diameters of reinforcements. The experimental results show that the new process is very efficient in increasing bond capacity of epoxy coated bars to concrete comparing those of traditional ones.

Abstract: At present, the finite element analysis has been an effective method to study the mechanical properties of steel bar drawing. In this paper, finite element analysis of the influence of bond strength on anchorage performance with concrete plastic damage model based on nonlinear analysis in ABAQUS was carried out. The finite-element analysis model of the single bar was established by using the finite element software ABAQUS. The Spring2 nonlinear spring element was introduced to simulate the interface of concrete and adhesive. Chemical anchorage bond slip constitutive model was determined by Spring2 element real constants. The nonlinear characteristics of concrete materials under the single reinforcement drawing could be described with the combination of the concrete plastic damage constitutive mode and nonlinear finite element methods. The nonlinear behavior of concrete under uniaxial tension of the action, especially the crack and stress distribution, could be accurately described. In order to study the influence of adhesive bond strength of chemically-bonded rebar mechanical properties, the constitutive relation of the bonded rebar slip of test results was referenced. The nonlinear property of spring was assigned by the bond slip relationship, embodied in the F-D curve of the spring. In order to analysis the influence of bond strength on anchorage performance, the slope of linear growth stage and the peak of nonlinear growth stage in bond slip relationship curve were changed.

Abstract: This paper deals with structural behavior of highly intelligent reinforced concrete (hereinafter, HIRC) beams actuated by embedded shape memory alloy wires through an extensive experimental program. The experiments were conducted under the monotonic loading condition. Based on the structural experiments involving HIRC, load-temperature deflection curve, ductility-effective depth, recovery, crack patterns, and failure mode comparison were made for investigative purposes. The results of the experiments confirmed that the ductility, recovery rates, and other properties of the HIRC specimens reinforced with SMA, wire mesh, fiber, and admixtures were superior to those of the unreinforced RCBs. The experimental results indicate that a good recovery rate in the HIRC beams could be obtained when the SMA wires were heated. Accordingly, the SMA wires could be potentially used for structural self-rehabilitation capability and deformation monitoring in architecture and civil structures.

Abstract: To evaluate and compare shear bond strength (SBS) and Adhesive Remnant Index (ARI) of orthodontic brackets polymerized by high-intensity light-emitting diode (LED) curing units at different intensities and curing times. Sixty extracted human upper premolar teeth were divided into 3 groups of 20 each. The tooth surfaces were prepared and the brackets were bonded on the teeth with light-cured adhesive and cured with 3 different light-curing units and conditions; Group 1 (Bluephase, 1,200 mW/cm², 20 seconds), Group 2 (VALO, 3,200 mW/cm², 6 seconds), Group 3 (FlashMax P3, 4,000-6,000 mW/cm², 3 seconds). Shear bond strength of the specimens were tested after bracket bonding for 5 minutes. The means of shear bond strength among groups were compared by Kruskal-Wallis and Mann-Whitney U tests. ARI were tested by the Fisher's exact test (p < 0.05). The means and standard deviations of SBS in groups 1, 2 and 3 were 21.80 ± 2.85, 21.04 ± 2.87 and 4.75 ± 2.82 MPa, respectively. Group 3 had significantly lowest mean SBS. Significant difference of ARI was found between Bluephase and VALO groups (p = .010). FlashMax P3 curing at 3 seconds generated significantly lowest mean SBS among 3 groups. The SBS generated by VALO curing at 6 seconds was not significantly different from Bluephase curing at 20 seconds. Therefore, VALO can be an option for orthodontic bracket bonding benefited in reducing clinician chairtime and patient discomfort.

Abstract: The effect of metal salt coating process on the bond strength of the bonded interface of 5052 aluminum alloy and 316L stainless steel was investigated by SEM observations of interfacial microstructures and fractured surfaces. Aluminum alloy surfaces were coated by boiling in 5% aqueous solution of NaOH for 5 s and 98% formic acid and 99.7% acetic acid for 20 s and 20 s respectively. Bonding process was performed at bonding temperature of 733 ~ 773 K under a pressure of 20 MPa (bonding time of 900 s). From this study, it is found out that the bonded strength of the joint increased with the rise in bonding temperature with or without metal salt coating process. However, it is understood that with metal salt coating process, high strength joint can be achieved with lesser deformation and lower bonding temperature. From the experimental results, it is found out that metal salt generation processing is effective at removing oxide film and substitution to a metal salt on the aluminum surface.

Abstract: This paper explores the effects of nanokaolinite clay (NKC) on the behavior of cement-based materials concrete. The resistance of NKC modified cement-based materials to freezing-thaw cycles and the corrosion processes of rebar embedded in the concrete were investigated. Ordinary Portland cement was partially substituted with NKC in ratios of 0%, 1%, 3%, and 5% by weight. The Rapid Freeze-Thaw Cabinet was used to measure the resistance of ordinary Portland cement concrete and concrete with clay to deterioration caused by repeated cycles of freezing and thawing, compressive strength were measured at regular intervals. The corrosion conditions of the rebar embedded in the concrete were studied by an electrochemical accelerated penetration system, pullout tests were performed to assess the bond properties including bond-slip curve, ultimate bond strength between concrete and rebar before and after corrosion. It is revealed that the introduction of NKC improves the freeze-thaw resistivity values and bond behavior in the concrete specimens compared to the control concrete; the corrosion of the rebar embedded in the concrete is impeded efficiently.

Abstract: The bond between prestressing (PS) steel and concrete plays an important role in pretensioned concrete members because the pretension force is directly transferred from PS steel to concrete by cutting or releasing the PS steels at the end of the members. While in capacity design approaches, designing for bond is considered to be a question of adequate strength along the bar length, in performance-based design approaches, the level of deformation as well as bond strength must be known and the bond-slip curves may give enough information. The purpose of this paper is to derive bond-slip curves for various tensioning forces within Korean design Code experimentally. For this purpose several series of tests have been conducted with different cover depths and tensioning forces. A realistic bond-slip curve is proposed which may be the base for more rational design of pretensioned concrete members.

Abstract: Researches on Ultra High Performance Concrete (UHPC) have been conducted worldwide owing to its outstanding durability and strength performances compared to normal concrete. This paper experimentally investigates the bond properties of reinforcements embedded in UHPC using direct pull-out tests. The specimens were prepared for various compressive strength levels of 120, 150, and 180MPa, diameters of reinforcements of 13, 16, 19, 22 and 25mm, cover to bar diameter ratios and bonded lengths. The influences of each test variable on bond properties are examined and may be a useful data for design and analysis of UHPC structures.