Adhesive Interface Failure Research Articles

Normal tensile bond behaviour of CFRP-epoxy laminate to concrete and steel

The effectiveness of CFRP sheets as external concrete reinforcement is determined by the CFRP-concrete bond behaviour. In this study the normal tensile bond of CFRP-epoxy laminate was assessed through the behaviour of the CFRP-concrete, and CFRP-steel bond. A pull-off apparatus combined with a newly introduced method using a clip-on displacement transducer was employed. The specimen was a field-impregnated single CFRP sheet attached to concrete and steel. The contribution of the epoxy was tested individually. The load-displacement behaviour, the ultimate strength, failure mode and the individual component's contribution to the CFRP bond, were analysed. The study concluded that for a concrete compression strength as high as 50 MPa the failure was designated by concrete rupture. For the CFRP-steel specimens, the failure was distinguished as adhesive interface failure or CFRP failure, influenced by the degree of epoxy impregnation and steel surface preparation. The load-displacement behaviour of the CFRP-concrete, CFRP-steel and epoxy were characterized by non-linearity with no post peak. The presence of CFRP sheets enhanced the stiffness of the individual epoxy. The presence of CFRP-epoxy has a negative affected to the normal tensile stiffness of concrete, but postponed the load levels at which first concrete cracking occur, regardless the concrete compression strength.

Pull‐off capacity of FRP–concrete composite bonded with epoxy/geopolymer at elevated temperature

AbstractExternally bonded strengthening technique to the concrete has been widely used with epoxy adhesive. However, the adhesive is considerably weak against high temperatures, which has been regarded as the critical point in the loss of integrity of the strengthened system. Alternatively, geopolymer materials have shown an excellent performance at high temperatures, thus, their potential to be used as adhesive material has been investigated in this work. In experimentation, the composite specimens were developed using both types of adhesives, epoxy and geopolymer, and their performance was evaluated at three temperature levels (20, 60, and 120°C) by conducting pull‐off strength tests and classifying their failure modes. It was observed that the strength of concrete and epoxy was reduced with temperature. In contrast, the strength of geopolymer‐based adhesives strength was increased due to the reactivity of the precursor at high temperatures. Also, bond strength was reduced for both composite specimens at elevated temperatures. The highest bond strength was observed for the epoxy‐based adhesive system at 20°C, and about 70% loss in bond strength was observed when exposed to 120°C. The failure mode was also shifted from concrete to adhesive interface failure, that is, failure between the adhesive and the fiber fabric layer. The geopolymer‐based adhesive system has lower strength than its counterpart at all temperature levels, and the failure mode was adhesive interface failure. To enhance the bonding capacity at high temperatures, efforts are being made by adding different minerals has been employed. From the experimental results, it was found that there were some improvements, however, it was still less than that of epoxy‐based system. Further optimization of the geopolymer adhesive using minerals is required and then high‐thermal resistance geopolymer adhesive can be established.

Effect of Nonwoven Carbon Tissue-Reinforced Epoxy Resin Adhesive Layer on the Single Lap Bonding Strength of Aluminum Alloy Joints.

The present paper provides a solution to enhance the reliability of bonding. The effect of the nonwoven carbon tissue (NWCT) composite adhesive layer on the bonding strength and reliability of aluminum alloy of single lap joints (SLJ) was investigated by embedding NWCT into the epoxy adhesive layer. The bonding strength, Weibull distribution, metallography of cross section, and fracture surface morphology of NWCT specimens were investigated. The results showed that the average bonding strength and Weibull characteristic strength (WCS) of NWCT-reinforced specimen were 16.78 and 17.17 MPa, which increased by 70.2 and 66.7%, respectively, compared with the neat specimen, and the Weibull modulus increased from 11.46 to 22.83, which indicated that NWCT specimens had higher bonding reliability. The mechanism of microcrack formation was obtained by analyzing the cross section of specimen loaded 95% WCS without macroscopic damage. The metallographic section showed that the microcrack of the neat specimen originated from the adhesive–aluminum interface, while the microcracks of the NWCT specimen originated from the interface between short carbon fibers (SCF) and adhesive. Typical failure modes were gained from visual observation and SEM. The failure mode of the neat specimen included more Al–adhesive interface failure, while the NWCT specimen included more internal failure of adhesive–SCFs with the fracture, pullout, peeling, and slippage of SCFs improving the toughness and bonding strength of the adhesive layer. The bridging effect of SCFs in the adhesive layer reinforced by NWCT can even the load and release the stress to improve the bonding reliability.

A numerical analysis of the fracture toughness in phase‐field modelling of adhesive fracture

AbstractWe propose and analyse a phase‐field model which allows for adhesive interface failure between two materials by a local reduction of the critical fracture toughness over a given length scale in the vicinity of the interface. A parameter study is carried out which reveals a significant dependence of the cracking behaviour on the ratio between the length scale of the crack phase‐field model and the width of the adhesive interface. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Microscale simulation of adhesive and cohesive failure in rough interfaces

Multi-material lightweight designs, e.g. the combination of aluminum with fiber-reinforced composites, are a key feature for the development of innovative and resource-efficient products. The connection properties of such bi-material interfaces are influenced by the geometric structure on different length scales. In this article a modeling strategy is presented to study the failure behavior of rough interfaces within a computational homogenization scheme. We study different local phenomena and their effects on the overall interface characteristics, e.g. the surface roughness and different local failure types as cohesive failure of the bulk material and adhesive failure of the local interface. Since there is a large separation in the length scales of the surface roughness, which is in the micrometer range, and conventional structural components, we employ a numerical homogenization approach to extract effective traction-separation laws to derive effective interface parameters. Adhesive interface failure is modeled by cohesive elements based on a traction-separation law and cohesive failure of the bulk material is described by an elastic-plastic model with progressive damage evolution.

Effect of Temperature Variation on Bond Characteristics between CFRP and Steel Plate

In recent years, application of carbon fiber reinforced polymer (CFRP) composite materials in the strengthening of existing reinforced concrete structures has gained widespread attention, but the retrofitting of metallic buildings and bridges with CFRP is still in its early stages. In real life, these structures are possibly subjected to dry and hot climate. Therefore, it is necessary to understand the bond behavior between CFRP and steel at different temperatures. To examine the bond between CFRP and steel under hot climate, a total of twenty-one double strap joints divided into 7 groups were tested to failure at constant temperatures from 27°C to 120°C in this paper. The results showed that the joint failure mode changed from debonding along between steel and adhesive interface failure to debonding along between CFRP and adhesive interface failure as the temperature increased beyond the glass transition temperature (Tg) of the adhesive. The load carrying capacity decreased significantly at temperatures approaching or exceedingTg. The interfacial fracture energy showed a similar degradation trend. Analytical models of the ultimate bearing capacity, interfacial fracture energy, and bond-slip relationship of CFRP-steel interface at elevated temperatures were presented.

The effect of depth and diameter of glued-in rods on pull-out connection strength of bamboo glulam

In order to explore bamboo glulam utilization in structure construction, the adhesive bonded steel connection of bamboo glulam was investigated in this study. By carrying out both-end pullout tests on glued-in threaded rods in bamboo glulam, the effects of depth and diameter of embedded rods in bamboo glulam on the pullout strength and the failure modes were discussed. Results showed that threaded rods fracture and adhesive interface failure were the two main different failure modes in the tests. The pullout peak load of both-end glued-in rods in bamboo glulam increased with the diameter and the embedded length of the threaded rods. To satisfy tensile load of the glued threaded rods (quality 4.8) used in the connections between engineering structural materials, the slenderness ratio (λ, the ratio of depth and diameter of glued-in threaded rods) equal to 10 or over was necessary.

Effect of Jig Design and Assessment of Stress Distribution in Testing Metal-Ceramic Adhesion.

In testing adhesion using shear bond test, a combination of shear and tensile forces occur at the interface, resulting in complex stresses. The jig designs used for this kind of test show variations in published studies, complicating direct comparison between studies. This study evaluated the effect of different jig designs on metal-ceramic bond strength and assessed the stress distribution at the interface using finite element analysis (FEA). Metal-ceramic (Metal: Ni-Cr, Wiron 99, Bego; Ceramic: Vita Omega 900, Vita) specimens (N = 36) (diameter: 4 mm, veneer thickness: 4 mm; base diameter: 5 mm, thickness: 1 mm) were fabricated and randomly divided into three groups (n = 12 per group) to be tested using one of the following jig designs: (a) chisel (CH) (ISO 11405), (b) steel strip (SS), (c) piston (PI). Metal-ceramic interfaces were loaded under shear until debonding in a universal testing machine (0.5 mm/min). Failure types were evaluated using scanning electron microscopy (SEM). FEA was used to study the stress distribution using different jigs. Metal-ceramic bond strength data (MPa) were analyzed using ANOVA and Tukey's tests (α = 0.05). The jig type significantly affected the bond results (p = 0.0001). PI type of jig presented the highest results (MPa) (p < 0.05) (58.2 ± 14.8), followed by CH (38.7 ± 7.6) and SS jig type (23.3 ± 4.2) (p < 0.05). Failure types were exclusively a combination of cohesive failure in the opaque ceramic and adhesive interface failure. FEA analysis indicated that the SS jig presented slightly more stress formation than with the CH jig. The PI jig presented small stress concentration with more homogeneous force distribution compared to the CH jig where the stress concentrated in the area where the force was applied. Metal-ceramic bond strength was affected by the jig design. Accordingly, the results of in vitro studies on metal-ceramic adhesion should be evaluated with caution. When adhesion of ceramic materials to metals is evaluated in in vitro studies, it should be noted that the loading jig type affects the results. Clinical observations should report on the location and type of ceramic fractures in metal-ceramic reconstructions so that the most relevant test method can be identified.

The characteristics of shear adhesive interface fracture of aluminum foam DCB bonded using a single-lap method

In this study, double cantilever beam (DCB) specimens made of aluminum foam were manufactured according to the BS 7991 and ISO 11343 standards. The thickness variable was set as t, and five specimens with thicknesses of 25~65 mm were manufactured. The manufactured aluminum foam DCB specimens were bonded using a single-lap joint method, and the force reaction due to forced displacement was determined. The five specimens had the maximum force reaction when the forced displacement was approximately 10~15 mm. The force reaction decreased rapidly once the maximum force reaction occurred. Subsequently, when the forced displacement increased by approximately 20 mm, the force reaction was negligible, i.e., adhesive strength disappeared. To evaluate the data obtained from the experiment, ANSYS was used to perform finite element analysis. The analysis results closely matched the experimental data. However, because there are limitations to the application of the viscosity of adhesives to actual construction structures, a small difference was observed from the time when the maximum force reaction occurred to the time of adhesive interface failure. The experimental results of the present study can be applied to actual complex structures to analyze their fracture behavior and to determine their mechanical characteristics.

Experimental Bond Performance of CFRP Anchors

In this paper, the technique: CFRP wrapping combined with CFRP anchors for RC structural member retrofit and its design criteria are introduced for a start. Experimental investigations [1,2, had been adopted and developed the use of CFRP anchors to provide confinement and improve square jacketing behaviors as well as prevent premature debonding for CFRP wraps. To fully determine the anchorage performance of CFRP anchor, a total of forty five specimens for the fiber bolt and the spread tail, two important components in CFRP anchor, were constructed and tested. The experimental results of failure modes were then discussed. For the fiber bolt, an analytical model for single metallic anchor and the best-fit equivalent bond stress were assessed with the test strength. The proposed design strength was also compared and validated the confidence. For the spread tail, the anchoring strength was tested limited due to the fiber rupture even more than the adhesive interface failure. As a result, the influence for the strength capacity of CFRP anchor was determined. The test data are helpful to analyze the behavior and modify the design criteria for the RC member retrofitted by the CFRP anchor technique.

Effect of cements ZOE on bond strength self adhesive resin cements

Purpose: The aim of this study is to evaluate the influence of the use of provisional cementations containing Zinc Oxide and Eugenol on bond strength of self-adhesive resin cements to dentin. Methods and materials: Thirty molars were divided into 6 groups (n=5). The materials used were: RelyX U100 (3MESPE) and Panavia F 2.0 (Kuraray) prior to permanent cementation, eugenol-containing provisional cements Provy (Dentsply) and eugenol-free RelyX Temp NE (3MESPE). To the temporary cementation discs acrylic resin were used in temporary cementation and kept for 7 days in distilled water at 37 ◦C for 24h. After this period, the crown and the temporary cement were removed and the teeth are cleaned. The permanent cementation of crowns composite resin (Herculite DA 3.5, Keer) wasmade with 6mm in height and cemented with resin cements according manufacturer’s. The buccal, lingual and proximal are light polymerization with a halogen lamp unit for 40 s each side. The specimenswere stored in distilledwater at 37 ◦C for 24h and then sectioned into sticks approximately 0.8mm. These were subjected to testing microtensile at the speed of 0.5mm/min in a universal testing machine (Instron 3342). The data were statistically analyzed using two-way ANOVA and Tukey’s tests (=0.05). After the tests, an analysis of fractured specimens will be held in stereomicroscope (10×) and MEV. Results: The cement Panavia showed highmeanmicrotensile bond strength (32.81±4.46) in control group. The presence of provisional cements reduces the bond strength only to Panavia cements. The U100 groups show the lowers bond strength values. Fractographic analysis shows the dentin–adhesive interface failure for all groups. Conclusion: The provisional cements must be avoided when used self-adhesive cements materials.

Geometry- and rate-dependent adhesive failure of micropatterned surfaces

The dynamic nature of adhesive interface failure remains poorly understood, especially when the contact between the two surfaces is localized in microscopic points of adhesion. Here, we explore the dynamic failure of adhesive interfaces composed of a large number of micron-sized pillars against glass. Surprisingly, we find a large influence of the microcontact geometry; ordered arrays of these pillars exhibit significantly stronger adhesive properties than equivalent surfaces in which the pillars are disordered. This can be understood with a simple geometric argument that accounts for the number of adhesive bonds that needs to be broken simultaneously to propagate the crack front. Moreover, the adhesive strength in both cases depends largely on the velocity with which the surfaces are separated. This rate dependence is explained on the basis of a semi-phenomenological model that describes macroscopic failure as a consequence of microscopic bond-rupture events. Our results suggest that the dynamics of adhesive failure, in the limit explored here, is predominantly stress-driven and highly sensitive to local geometry effects.

POSTBUCKLING DEGRADATION FE ANALYSIS OF STIFFENED COMPOSITE PANELS

The capability of a commercial industrial tool, ABAQUS, to simulate the critical damage mechanisms in stiffened composite panels has been evaluated. The analysis and conclusions are supported by experimental results. The focus is on skin–stringer separation during compressive loading. Results show that the advanced degradation modeling capabilities present in commercial codes today may lead to an accurate characterization of the deep postbuckling range behavior and the collapse of stiffened composite panels. Compared to current design practice, where the first indication of ply failure or the onset of damage propagation is taken as the failure load, the methods used here provide a way to exploit the reserves in composite structures. It is concluded that implementing degradation mechanisms (composite ply and adhesive interface degradation) presents a significant improvement to simulate accurately the deep postbuckling states and collapse for stiffened composite panels with adhesively bonded stringers. The nature of the final loss of load-carrying capacity for this type of structures, by composite ply and adhesive interface failure, driven by postbuckling deformation, makes this simulation approach essential.

Chemical adhesion rather than mechanical retention enhances resin bond durability of a dental glass-ceramic with leucite crystallites

This study aims to evaluate the effect of chemical adhesion by a silane coupler and mechanical retention by hydrofluoric acid (HFA) etching on the bond durability of resin to a dental glass ceramic with leucite crystallites. Half of the ceramic plates were etched with 4.8% HFA (HFA group) for 60 s, and the other half were not treated (NoHFA group). The scale of their surface roughness and rough area was measured by a 3D laser scanning microscope. These plates then received one of the following two bond procedures to form four bond test groups: HFA/cement, NoHFA/cement, HFA/silane/cement and NoHFA/silane/cement. The associated micro-shear bond strength and bond failure modes were tested after 0 and 30 000 thermal water bath cycles. Four different silane/cement systems (Monobond S/Variolink II, GC Ceramic Primer/Linkmax HV, Clearfil Ceramic Primer/Clearfil Esthetic Cement and Porcelain Liner M/SuperBond C&B) were used. The data for each silane/cement system were analyzed by three-way ANOVA. HFA treatment significantly increased the surface Ra and Ry values and the rough area of the ceramic plates compared with NoHFA treatment. After 30 000 thermal water bath cycles, the bond strength of all the test groups except the HFA/Linkmax HV group was significantly reduced, while the HFA/Linkmax HV group showed only adhesive interface failure. The other HFA/cement groups and all NoHFA/cement groups lost bond strength completely, and all NoHFA/silane/cement groups with chemical adhesion had significantly higher bond strength and more ceramic cohesive failures than the respective HFA/cement groups with mechanical retention. The result of the HFA/silane/cement groups with both chemical adhesion and mechanical retention revealed that HFA treatment could enhance the bond durability of resin/silanized glass ceramics, which might result from the increase of the chemical adhesion area on the ceramic rough surface and subsequently reduced degradation speed of the silane coupler, rather than the mechanical retention of the ceramic rough surface.