The paper presents experimental research and numerical modeling of dynamic properties of magnetorheological elastomers (MREs). Isotropic and anisotropic MREs have been prepared based on silicone ...matrix filled by micro-sized carbonyl iron particles. Dynamic properties of the isotropic and anisotropic MREs were determined using double-lap shear test under harmonic loading in the displacement control mode. Effects of excitation frequency, strain amplitude, and magnetic field intensity on the dynamic properties of the MREs were examined. Dynamic moduli of the MREs decreased with increasing the strain amplitude of applied harmonic load. The dynamic moduli and damping properties of the MREs increased with increasing the frequency and magnetic flux density. The anisotropic MREs showed higher dynamic moduli and magnetorheological (MR) effect than those of the isotropic ones. The MR effect of the MREs increased with the rise of the magnetic flux density. The dependence of dynamic moduli and loss factor on the frequency and magnetic flux density was numerically studied using four-parameter fractional derivative viscoelastic model. The model was fitted well to experimental data for both isotropic and anisotropic MREs. The fitting of dynamic moduli and loss factor for the isotropic and anisotropic MREs is in good agreement with experimental results.
•Dynamic properties of isotropic and anisotropic magnetorheological elastomers (MREs) were measured using double-lap shear test.•Dynamic moduli of the MREs reduce with raising the strain amplitude. Dynamic stiffness and damping of the MREs increase with the rise of the frequency.•The magnetorheological (MR) effect, dynamic stiffness and damping of the MREs enhance with increasing the magnetic flux density.•The anisotropic MREs showed higher dynamic moduli and greater MR effect than those of the isotropic ones.•Dependence of MRE dynamic properties on frequency and magnetic intensity was numerically studied by fractional derivative viscoelastic model.
This paper presents the results of an investigation on the bond behavior and stress-transfer mechanism of polyparaphenylene benzobisoxazole (PBO) fiber-reinforced cementitious matrix (FRCM) ...composites bonded to a concrete substrate using double-lap and single-lap shear tests. Results of double-lap shear tests with different composite bonded lengths and widths are presented and compared with those from single-lap shear tests previously reported by the authors. The idealized load response developed from single-lap shear tests is found to characterize the response of the composite in double-lap shear tests, although with a few key differences. With the double-lap shear test, load redistribution among the composite strips influences the post-peak response if debonding does not occur equally in both strips. Values of the ultimate (peak) stress determined using double-lap shear tests are generally consistent with, although slightly lower than, those determined by single-lap shear tests when the bonded length is longer than the effective bond length.
This paper aims to investigate the interface efficiency of Carbon Fiber Reinforced Polymers (CFRP) adhesively bonded on concrete, a commonly used retrofitting measure applied for enhancing the ...deformability and strength of decaying structures or existing ones with low capacity. The efficiency quantification is expressed with the Interface Capacity Index (IC). The index correlates the thickness and strength of each layer of the strengthening system and accounts for the transferred loads (ICL) and the strain distribution that causes the failure propagation on the concrete substrate (ICfp). The investigation focuses on different CFRP strengthening schemes (laminated fabrics, prefabricated plates, Near Surface Mounted bars-NSM) applied to concrete substrates using different adhesive layers. Two cases were studied for different levels of concrete’s integrity: (a) healthy and (b) containing corrosion products. The experimental results were used to calibrate the numerical models and to evaluate the effects of different strengthening strategies. The results show the tendency of the strengthening systems to shift the interface performance from fully elastic to non-linear. Further, the quantification of the efficiency of retrofitting can be addressed by accounting for the mechanical and geometrical properties at the interface level, representing different failure modes and integration levels.
Understanding and predicting the behaviour of bonded joints under different loading conditions is certainly an aspect of primary importance. Although numerous experimental studies have been carried ...out over the last few decades, the shear behaviour of bonded joints under cyclic loading has not been investigated in detail. To fill this gap, an extensive experimental and numerical program of double lap shear bonded joints has been carried out. The double lap shear joints were tested under static and cyclic loading to evaluate and compare the influence of external forces on the adhesive performance. The results are discussed in terms of the force-displacement relationship, shear stress, stiffness, residual displacement, and initial damage. Finally, a method is presented for predicting the actual behaviour of double lap shear bonded joints under different loading conditions using an imperfect interface model with damage evolution. The numerical results are in good agreement with the experimental results for all loading conditions. This work has provided and validated an interesting design tool for adhesive structures.
This study investigates timber connections with flexible polyurethane adhesives, which prove to have the potential for timber-adhesive composite structures without mechanical connections for seismic ...regions. Results of conducted cyclic double lap-shear adhesive timber joints tests were compared with available experimental results on timber connections with standard mechanical dowel-type fasteners and with results of numerical finite element analysis. The study found that the shear strength, elastic stiffness and strength degradation capacity of the flexible adhesive connections were significantly higher compared to mechanical fasteners commonly used in seismic-resistant timber connections. The latter, however, manifested larger ultimate displacements but also yielded at lower displacements.
The purpose of this study is to investigate the influence of adhesive types on the interfacial behavior of externally bonded basalt fiber reinforced polymer (BFRP) sheet-concrete substrate. Twelve ...manufactured double-lap shear samples were tested using four bonding adhesives. The strains on the surface of BFRP‐concrete joint were determined using electrical resistance strain gauge together with two‐dimensional digital image correlation technique (2D‐DIC). Experimental results show that properties of different bonding adhesives i.e., stiff (linear elastic, higher strength) and soft (nonlinear elastic, lower modulus, higher ultimate strain) has a significant impact on the failure mode, stiffness, ultimate load, strain and shear stress distribution nonetheless not so much on bond-slip relationship. The failure modes of specimens changed from interfacial debonding or cohesive failure in concrete substrate for stiff adhesive specimens to debonding in adhesive layer when soft adhesives are used. Stiff adhesive interfaces experienced higher ultimate loads from 1.1 to 1.3 times higher than soft adhesive interface. Meanwhile soft adhesives are shown to possess a lower maximum shear stress, higher interfacial fracture energy and longer stress transfer length.
•Lab and field bond tests are carried out on SRG applied to convex masonry substrates.•SRG-to-substrate bond behaviour is improved by compressive normal stresses induced by curvature.•Bond strength ...increases with the increase of substrate curvature and bond length.•Cord-to-matrix interlocking is crucial for the effectiveness of the reinforcement.•Bond behaviour is independent from the mechanical properties of the vault substrate.
Steel Reinforced Grout (SRG), consisting of ultra high tensile strength steel cords embedded in a mortar matrix, is an effective solution for the upgrade of existing structures. Among its various applications, it can be applied to the extrados and the intrados of masonry vaults to improve their load-carrying and seismic capacity. Nevertheless, its bond strength on curved substrates, which is crucial for the design of the reinforcement of masonry arched members, has not been properly explored yet. This paper presents an experimental investigation on the bond behaviour of SRG applied to convex masonry substrates. Double-lap shear bond tests were carried in the laboratory on small-scale brickwork specimens to investigate the effect of curvature radius, bond length and textile architecture on bond strength and failure mode. Full-scale field tests were performed to study the bond behaviour and the resisting mechanisms of SRG applied to the extrados of an existing masonry vault, taking into account the actual substrate preparation and mortar curing conditions at a construction site.
Magnesium orthopaedic fracture fixation devices can potentially provide significant clinical benefits, such as the elimination of secondary surgeries for device removal due to in-vivo resorption and ...reduced stress shielding due to reduced device stiffness. However, development, approval, and clinical adoption of magnesium devices has been hindered by the excessively high rates of in-vivo corrosion such that the structural integrity of the device can be catastrophically reduced before fracture healing occurs. Coating of devices with calcium phosphate coatings has been shown to significantly reduce corrosion rates, while enhancing osseointegration. However, the adhesion strength between the CaP coatings and magnesium substrates has not been previously investigated. Clinical insertion of fracture fixation devices such as intramedullary nails and k-wires will impose significant shear loading on the coated surface of the implant. If the effective shear strength of the coating-device interface is not sufficiently high, the coating will be damaged and removed during device insertion. In the current study a bespoke experimental-computational approach is developed to provide a new understanding of the relationship between coating thickness, surface roughness, and effective shear strength of the CaP coating- Mg substrate interface. Nine test cases were created by adjusting either the deposition time (3 thickness values) or the surface treatment of the Mg alloy using SiC paper (3 roughness values) and double-lap shear testing was performed for these coating configurations. Strain development in the Mg substrates was monitored using strain gauges, and failure stress was determined for each configuration. Test results revealed that the effective shear strength of the coating-substrate interface is significantly higher for coatings on the rougher substrate surfaces when compared to those on smoother surfaces. Coating thickness was not found to significantly influence the effective shear strength over the range considered in this study (0.37–1.34 μm). Micro-scale finite element models of lap-shear tests were constructed using experimental profilometry data. Simulations of rough coating-substrate interfaces reveal that significant localised compression occurs at the coating-substrate interface in regions of large asperities. A novel cohesive zone formulation has been developed to simulate compression induced shear hardening, and the resultant simulations are found to accurately predict the significantly higher effective shear strength measured experimentally for rougher coatings compared to smoother Mg substrate surfaces.
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•Novel lap shear experiment studying the relationship between coating thickness, implant surface roughness and shear strength.•First cohesive zone model to incorporate shear hardening due to interface compression.•Regions of high interface compression at asperities in rough coatings, results in locally elevated interface shear strength.
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•Laminated glass double-lap shear specimens with four interlayers were tested.•The type of interlayer material affected the maximum load and breakage mode.•Humidity and long-term UV ...radiation had a negative effect on some specimens.•The strength either increased or remained unaffected by thermal cycles.•The stress distribution was not homogeneous in the glass-interlayer interface.
Laminated glass is a composite laminate obtained from combining two or more glass layers with a polymeric interlayer. The adhesion between glass and interlayer, as well as the shear strength and stiffness of the interlayer, are key factors to evaluate the cohesive behaviour of laminated glass. Glass is a very durable material, while polymeric interlayers can be deteriorated by exposure to weathering factors. A double-lap shear test was carried out on laminated glass specimens, with four different interlayer materials (PVB BG-R20, Saflex DG-41, SentryGlas, and EVASAFE), after different ageing tests (unaged, thermal cycles, humidity, and UV radiation). The material selection affected the shear behaviour of the bond between glass and interlayer, and so did the previous exposure to certain ageing factors. Since the polymeric interlayers are viscoelastic materials, and therefore its mechanical properties are time- and temperature-dependant, the results here presented should be complemented with dynamic and static tests at different temperatures.
•Compiled database of CFRP/steel bonded double lap joints that failed by debonding.•Quantified model uncertainty for the Hart-Smith model for thin outer adherends.•Calculated reliability indices, ...resistance factors for multiple joint configurations.•Demonstrated the importance of each joint parameter to the debonding variability.
This paper presents the details of a reliability-based analysis of bonded double-lap shear (DLS) joints between steel and carbon fiber reinforced polymer (CFRP) composites. A comprehensive database of experimental results of CFRP-to-steel DLS joints is compiled and a probabilistic analysis of the data is conducted. The compiled experimental results are compared with the bond strengths predicted by the Hart-Smith model for thin adherends and the model uncertainty is characterized, for five popular structural epoxy adhesives and two types of surface preparation techniques. Considering the mechanical and geometrical uncertainties of constituent materials, two reliability-based approaches, First-Order Reliability Method (FORM) and Monte-Carlo Simulation (MCS), are used to calculate the resistance factor at a target reliability index of 3.5. It is found that these two approaches agree well and the resistance factor varies with adhesives, surface preparation techniques, and CFRP types. The importance vector of random variables reveals that the adhesive shear ductility is the most influential material property in determining the reliability index of the bonded joints.
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