Double Shear Test Research Articles

Characterization of natural – Synthetic fiber reinforced epoxy based composite – Hybridization of kenaf fiber and kevlar fiber

The work deals with the mechanical characterization of Kenaf and Kevlar fiber reinforced epoxy-based composites. The tensile, flexural, double shear, impact, hardness and de-lamination tests were conducted on composite laminates developed through hand lay-up process. Morphological analysis was conducted to examine the split surface of the tested specimen. The experimental investigation reveals that the mechanical properties of epoxy composites were enhanced by the hybridization of Kenaf and Kevlar fiber.

Study on bond strength of geopolymer and control concrete between fiber‐reinforced polymer and steel bars

AbstractSignificant issue in reinforced concrete (RC) structures is corrosion of steel. High alkalization of cement matrix, low permeability, and sufficient cover plays an important role to shield from corrosion of steel. There is a replacement material for steel is fiber‐reinforced polymer (FRP) bars as reinforcement. The FRP bars are nonconductive and durable material and they are composited from fibers and polymers matrix. In this study, new technology geopolymer concrete (GC) was used along with glass fiber‐reinforced polymer (GFRP) and basalt fiber‐reinforced polymer (BFRP) bars. GC is produced from industrial by‐product materials such as fly ash and ground granulated blast furnace slag (rich in silica and alumina) and treated as sustainable material. The long term durability of many RC structures affects drastically by the reinforcement corrosion. Main aspect of bond behavior is tension stiffening as it has capability to control the reinforcement to shift the tensile stresses to concrete. This paper evaluates the bond strength between the GC reinforced with GFRP/BFRP and the results were evaluated with conventional concrete (CC) reinforced with steel. The pullout test method was used to determine the bond between FRP and steel bars with the surrounding concrete based on IS: 2770 (part I)‐1967. The comparison of bond strength GC with FRP almost same as CC with steel. The tension test and double shear test were also carried out in FRP and steel bars based on IS 432–1982 and 5242–1979, respectively.

Testing methods for shear strength of bond line between concrete and different types of engineered wood

This paper identified a reliable testing method for determining the shear strength of bond lines between concrete and engineered wood. The identification was carried out based on analytical derivations and experimental tests on concrete (compressive strength of 24.8 MPa) and engineered wood composite connections glued by two types of epoxy. Forty specimens were tested under two commonly used test setups, i.e. 20 double-shear tests on timber-concrete composite specimens with a bond length of 50 mm and another 20 compression-shear tests on specimens with a bond length of 300 mm. The result analysis showed that there was no significant statistical difference between the shear strength of the bond lines (around 2.3 MPa) as well as between the failure modes obtained (dominated by concrete failure), regardless of the considered bond lengths and adhesive types investigated. The analysis used a quasi-non-linear fracture mechanics model, considering the boundary conditions of the tests. The analytical model revealed that the ultimate shear stress is approximately uniformly distributed both in the double-shear and in the compression-shear tests, so the spatially averaged shear stress value can approximate the critical shear stress of the bond line with sufficient accuracy. However, if the failure occurred in the wood or the strength of the concrete was higher, the shear stress distribution at ultimate load in the compression-shear tests with a bond length of 300 mm would not be uniform. The maximum shear stress value, which is significantly larger than the average one, occurred at the fixed (or supporting) end of the bond line. Even so, in the shear tests with a bond length of 50 mm, the average ultimate shear stress value was still close to the shear strength with a difference smaller than 5%. Hence, a bond length of 50 mm is recommended for determining the shear strength of a bond line between normal strength concrete and engineered wood when using a push-out shear test setup.

Influence of Aluminum Surface Treatment on Tensile and Fatigue Behavior of Thermoplastic-Based Hybrid Laminates.

Hybrid laminates consist of layers of different materials, which determine the mechanical properties of the laminate itself. Furthermore, the structure and interfacial properties between the layers play a key role regarding the performance under load and therefore need to be investigated in respect to industrial applicability. In this regard, a hybrid laminate comprised of AA6082 aluminum alloy sheets and glass and carbon fiber-reinforced thermoplastic (polyamide 6) is investigated in this study with a focus on the influence of aluminum surface treatment application on tensile and fatigue behavior. Four different aluminum surface treatments are discussed (adhesion promoter, mechanical blasting, phosphating, and anodizing), which were characterized by Laser Scanning Microscopy. After the thermal consolidation of the hybrid laminate under defined pressure, double notch shear tests and tensile tests were performed and correlated to determine the resulting interfacial strength between the aluminum sheet surface and the fiber-reinforced plastic, and its impact on tensile performance. To investigate the performance of the laminate under fatigue load in LCF and HCF regimes, a short-time procedure was applied consisting of resource-efficient instrumented multiple and constant amplitude tests. Digital image correlation, thermography, and hysteresis measurement methods were utilized to gain information about the aluminum surface treatment influence on fatigue damage initiation and development. The results show that fatigue-induced damage initiation, development, and mechanisms differ significantly depending on the applied aluminum surface treatment. The used measurement technologies proved to be suitable for this application and enabled correlations in between, showing that the hybrid laminates damage state, in particular regarding the interfacial bonding of the layers, can be monitored not just through visual recordings of local strain and temperature development, but also through stress-displacement hysteresis analysis.

Evaluation of Functionalized Coatings for the Prevention of Ice Accretion by Using Icing Wind Tunnel Tests

Ice accretion presents serious safety issues, as airplanes are exposed to supercooled water droplets both on the ground and while flying through clouds in the troposphere. Prevention of icing is a main concern for both developers and users of aircraft. The successful solution of this problem implies the combination of active and passive methods and the use of advanced sensors for early detection of icing and monitoring of ice accretion and de-icing processes. This paper focuses on the development of passive solutions. These include advanced anti-icing coatings deposited by a variety of chemical methods including sol-gel, advanced paints based on polyester combined with fluorinated derivatives and applied by electrostatic spray deposition and conventional silicone-based paints modified by adding alumina nanoparticles. Water contact angle has been measured in all cases, demonstrating the hydrophobic character of the coatings. An ice accretion test has been carried out in a laboratory scale icing wind tunnel (IWT) located in a cold climate chamber. Three different studies have been undertaken: ice accretion measurement, durability of the anti-icing behavior after several icing/de-icing cycles and ice adhesion testing by means of the double lap shear test (DLST) methodology. All the studied coatings have shown significant anti-icing behavior which has been maintained, in some cases, beyond 25 cycles. Although these results are still far from any possible application for aeronautic components, they provide interesting insights for new developments and validate the laboratory scale tests.

A new method for joining metal and polymer sheets in sandwich panels for highly improved interface strength

Wire mesh interlayers are introduced to fabricate high interface strength metal-polymer-metal sandwich panels. While resistance welding is used to join metal sheets to wire mesh at predesignated spots, vacuum hot pressing is used to infuse polymer into the wire mesh. Peel strength for fabricated sandwich panels is seen to be around 300% higher than that for adhesive joints reported in literature. Since, interface strength is achieved from welding and mechanical interlocking, it does not degrade in presence of moisture. Uni-axial tensile tests are used to characterize strength and elongation of individual layers and fabricated sandwich panels. Interface strength is characterized using peel and double lap shear tests. V-bending and stretch forming experiments are used to demonstrate formability of the developed sandwich panels. The presented method is an attractive alternative to use of adhesives for joining of metals to polymers.

Analytical modelling of bond-slip failure between epoxy bonded FRP and concrete substrate

In this paper, a set of explicit theoretical derivations from a generalised bond-slip model for an epoxy bonded fibre reinforced polymer (FRP) sheet to concrete are presented. The derivations address the maximum bond resistance, load-slip response, effective bond length and stress–strain distributions along the FRP. The generalised bond-slip model was compared with the existing bond-slip models to obtain the optimal bond-slip parameter using bond resistance results of single and double lap shear tests results available in the literature. The theoretical predictions using the optimal bond-slip parameters showed good agreement with experimental results of double lap shear tests. Furthermore, in order to understand the influence of the bond-slip parameters, a series of parametric studies are presented. Overall, the proposed bond-slip model and explicit derivations provide complete understanding of bonded FRP on concrete, as opposed to the partial understanding provided by empirical and semi-empirical models available in the literature.

Evaluation of spalling of concrete pieces from tunnel lining employing joint shear model

This paper was conducted to quantify the spalling of tunnel lining concrete. This paper firstly modeled the spalling of tunnel lining concrete and examined ways to quantitatively evaluate the safety of the tunnel lining concrete against spalling by comparing the shear stress acting on the joint surfaces of lining concrete cracks with the shear capacity of the joint surfaces. Secondly, based on double shear tests simulating the spalling phenomenon, it was found that wider crack widths as well as greater tapered angles of the joint surfaces resulted in lower shear capacities. Thirdly, a method for simulating the shearing process of joint surfaces was proposed. The method was shown to be able to roughly estimate the relationship between the joint aperture and the shear capacity. Using the improved method, the shear capacity was considered using various widths and tapered angles of the cracks. Furthermore, it was found that the JRC value of the joint surface samples collected from actual tunnels was between the JRC value of the mortar beam joint surfaces that were made in the shear test and that of the joint surfaces of the concrete beam, made in the shear tests with the maximum aggregate size measuring 40 mm. A parameter study was also conducted under hypothetical conditions for the relationship between the width of the cracks and the safety of the tunnel lining against spalling.

Mechanical and thermal properties of PVC and polyurethane foam hybrid composites

Abstract Sandwich foam composites are mostly used today in structural applications in aerospace and automobile industries due to light weight and high stiffness of the sandwich composites. In this research work, the composites were fabricated by using polyurethane and PVC foam and carbon fiber as skin. Sandwich composites were fabricated by the hand lay-up method. Mechanical tests such as tensile, flexural, impact, double shear, inter delamination and hardness tests were conducted. A thermo gravimetric analysis (TGA) test was also performed for the analysis of the temperature characteristics of the sandwich composites. The internal structures of tested samples were analyzed through a scanning electron microscope (SEM). The results show that the tensile, flexural, impact, thermal and inter delamination strengths of PVC foam composites are superior to those of other composites.

Influence of the bonding of rebar dowel with adhesive on wood–concrete composite specimens

Ensuring the quality of the connector used in wood–concrete composite systems is a critical factor affecting the performance of the system. The main objective of this research was to study the strength and stiffness of wood–concrete composite specimens with two types of rebar dowel connectors: fixed to the wood (solid timber) using epoxy adhesive and by pre-drilling on smaller diameter holes in the wood (without the use of adhesive). In the composition of the test specimens, rebar dowels of 12·7 mm dia. were used. The strength and stiffness of the connectors were determined by double shear tests, performed on composite specimens. Statistical analysis was used to compare the results obtained and regression models were proposed for estimating the stiffness parameters of the connections. The connectors glued with epoxy adhesive provided better strength and stiffness for the composite specimens when compared to the connectors fixed to the wood by pre-drilling. The differences between the strength and stiffness of the connection systems analysed were statistically significant. The regression models proposed presented a good approximation for the estimation of the Kser and Ku slip moduli of the composite specimens analysed.

Hard Quasicrystalline Coatings Deposited by HVOF Thermal Spray to Reduce Ice Accretion in Aero-Structures Components

Weather hazards, in particular icing conditions, are an important contributing factor in aviation accidents and incidents worldwide. Many different anti-icing strategies are currently being explored to find suitable long-lasting solutions, such as surface engineering, which can contribute to reduce ice accumulation. Quasicrystals (QCs) are metallic materials, but with similar properties to those of ceramic materials, such as low thermal and electrical conductivities, and high hardness. In particular, QCs that have low surface energy are commercially used as coatings to replace polytetrafluoroethylene (PTFE), also known as Teflon, on frying pans, as they do not scratch easily. PTFE exhibits excellent anti-wetting and anti-icing properties and therefore QCs appear as good candidates to be employed as ice-phobic coatings. Al-based QCs have been applied by High Velocity Oxyfuel (HVOF) thermal spray on typically used aeronautic materials, such as Ti and Al alloys, as well as steels. The coatings have been characterized and evaluated, including the measurement of hardness, roughness, wetting properties, ice accretion behavior in an icing wind tunnel (IWT), and ice adhesion by a double lap shear test. The coatings were studied, both as-deposited, as well as after grinding, in order to study the effect of the surface roughness and morphology on the ice accretion and adhesion properties. The QC coating was compared with PTFE and two polyurethane (PU)-based commercial paints, one of them known to have anti-icing properties, and the results indicate an ice accretion reduction relative to these two materials, and ice adhesion lower than bare AA6061-T6, or the PU paint in the ground version of one of the two QCs. Since the QC coatings are hard (GPa Vickers hardness > 5), a durable behavior is expected.

Experimental Study of Indonesian Low-Cost Glass Fiber Reinforced Elastomeric Isolators (GFREI)

In this research, four specimens of elastomeric base isolators were tested. They were named as A1, A2, B1, and B2. The type A and B elastomeric isolators were made from the hyperelastic rubber with the hardness of 40 and 60, respectively, according to the durometer scale shore A. Prior to the making of elastomeric isolators, both rubber categories (40 and 60) were tested to obtain the mechanical properties of these types of hyperelastic rubbers. testing of hyperelastic rubbers and elastomeric isolators were carried out following BS EN 15129:2009 requirements. The A1 and B1 specimens were tested under vertical load. For lateral load tests, double shear tests were carried out. Specimen A1 which has been tested under vertical load previously was used to be combined with Specimen A2 and tested under lateral load. This double shear test was also conducted to Specimens B1 and B2 in which B1 has been tested earlier under vertical loading. From the results of the hyperelastic rubber tests, the elongation at the breaking of type A and B rubbers were more than 500 and 400 percent with the maximum stress of 8.8 and 6.2 MPa, respectively. While the testing results of type B elastomeric isolators showed better damping ratio than type A, the effective stiffnesses of type A elastomeric isolators were found higher than type B. From the test results; it can also be shown that higher-story buildings, which have high axial forces, might use type B elastomeric isolators which have higher hardness and damping ratio, whereas low-rise buildings with low axial forces can use type A elastomeric isolators. Thus, it can be concluded that the Indonesian rubber has a bright future and has a strong potential to be developed for use in the production of low-cost elastomeric isolators.

Bonding behavior between reactive powder concrete and normal strength concrete

In order to investigate the bonding behavior between reactive powder concrete (RPC) and normal strength concrete (NSC), splitting tensile test of 81 specimens and double shear test of 27 specimens were conducted, the effects of water-to-binder ratio (W/B) of RPC, steel fibre volume fraction, and interfacial roughness on RPC-to-NSC bonding were investigated. The results showed that the interfacial roughness was the most important factor affecting the bonding shear strength and splitting tensile strength, followed by the RPC W/B, and finally the steel fibre volume fraction. The increase of interfacial roughness in the range of 2.11–6.01 mm and the steel fibre volume fraction in the range of 1%-2% can improve the splitting tensile strength and shear strength. The effect of RPC W/B increase in the range of 0.2–0.24 on the splitting tensile strength was positive, but the shear strength increased first and then decreased with the increase of RPC W/B, the maximum shear strength appeared at 0.22 W/B. Based on the test result, a NSC-RPC shear strength formula considering the interfacial treatment was proposed.

Evaluation of Warm Mix Asphalt Performance Involving Synthetic Zeolite

Warm mix asphalt (WMA) blends at temperatures lower than those in conventional mixtures by 20-50 °C. Many additional advantages, such as a reduced susceptibility to permanent deformation, have exhibited when synthetic zeolites were used as a warm mix asphalt additive. In this research, the best gradation of aggregate was selected, and optimum asphalt content was determined for asphalt concrete layer (surface course) according to Superpave design system. All mixtures were evaluated with some tests which include Marshall characteristics, moisture damage of asphalt mixtures, Immersion–Compression, double punch shear and wheel tracking test. To compact asphalt mixtures with (100 and 150) mm in diameter, Superpave Gyratory Compactor (SGC) was used. Five different percentages (3, 4, 5, 6 and 7) of synthetic zeolite were used for preparation of warm mixes to compare with hot mixture for the effect of different percentage of synthetic zeolite on performance asphalt mixture in terms of water sensitivity. The experimental work’s results indicated that the mixture properties were affected by selected percentages of synthetic zeolite to the warm asphalt differently. The WMA mixture with 5 % of synthetic zeolite decreased the rut depths of the mixtures with increase in the punching strength of the mixtures and slight increase in the tensile strength ratio (TSR), compressive strength and index of retained strength (IRS).

Double Shear Load Carrying Capacity of Kempas and GFRP Dowelled Connections

Glass fibre reinforcement polymers (GFRP) application for reinforcement of wood, concrete and steel member is relatively becoming more variety in construction applications. Although it is possible to build large monolithic structures with composite materials, there are still several reasons for the structure to fail. One of the main reasons that contribute to this failure is the connection performance due to its function in carrying load across the structure. Thus having the right fundamental data for connection design purposes according to the specific and technological upgraded materials is very important. One of the basic methodologies in gaining the design data is through experimental double shear test which can be verified by European Yield Model (EYM) theory. Therefore, the objective of this research is to determine the load carrying capacity of double shear strength behaviour connections made of Kempas timber species as the main member and dowelled by the GFRP or the Kempas rod. The specimens were tested under the shear load with 2mm/min rate and tested until failure. From the experiment, it was found that the average ultimate shear strength of member dowelled with GFRP rod is 21.36% higher compared to one doweled with Kempas rod. According to mode of failure between two types of bolt, GFRP dowelled performs well (Mode I& IV) rather than Kempas dowelled (Mode IV).

Analisa Kekuatan Tahanan Lateral Pada Sistem Komposit LVL Kayu Sengon dan Beton Pracetak

LVL Sengon and concrete can be used to form a composite structure of the floor system. Connections between LVL Sengon and concrete on this composite floor system are the weakest part so that a majority of structural damages are concentrated at these joints. This study discusses the lateral resistance of lag screw joints in a composite system of LVL Sengon and precast concrete. The lateral joint resistance was evaluated through quasi-static loading upon double shear test specimens having two screws at every single shear. Variation of the specimens includes precast concrete compressive strength of 20.71 MPa and 25.29 MPa, screw diameter of 6 mm length 101.6 mm and 8 mm length 101.6 mm and 127 mm, and angle of lag screw axis against the wood fiber of 60° and 90°. The result shows that lateral resistance of the test is greater than that of EYM, SNI, and EC5 predictions. Joint failure in this experiment is due to failure in wood fiber along with the occurrence of one up to two plastic hinges in the screw.

Performance Evaluation of GFRP Rock Bolt Sensor for Rock Slope Monitoring by Double Shear Test

This study aims to evaluate the sensing performance of glass fiber‐reinforced polymer (GFRP) rock bolt sensors instrumented with strain gauges for monitoring rockslides. Experimental studies are conducted with four different types of GFRP rock bolt sensors and concrete blocks having central holes and two shear joints. Two GFRP rock bolt sensors are inserted into holes and then fixed in concrete blocks with cement grout and soil, respectively. The other two are coated with heat‐shrink tubes to protect strain gauges and wires, which are then fixed in concrete blocks with cement grout and soil, respectively. Double shear tests are performed to produce shear deformations of GFRP rock bolt sensors, and then strain change with shear displacement is monitored. The results manifest that the variation in strain with shear displacement is more sensitive in the GFRP rock bolt sensor fixed with soil than with cement grout. Also, strain gauge wires in the GFRP rock bolt sensor fixed with cement grout are broken earlier than with soil. Furthermore, it is confirmed that the heat‐shrink tube effectively protects strain gauges and wires, so that GFRP rock bolt sensors coated with heat‐shrink tubes work for a longer time than the uncoated sensors. The present study shows that the GFRP rock bolt sensor can be useful for monitoring rock slope failure.

Boron nitride inclusions within adhesive joints: Optimization of mechanical strength and bonded defects detection

Non Destructive Testing (NDT) by active InfraRed Thermography (IRT) of bonded Carbon Fibers Reinforced Plastic (CFRP) laminates is a very challenging issue. Adding Boron Nitride (BN) particles within the joint material provides an interesting solution to better capture bonding defects. Though increasing additives leads to the improvement of NDT, the validation of this solution requires the mechanical characterization of the new joint material. In this way, the influence of particles on the mechanical properties of the adhesive joint is first investigated via double strap lap shear tests for different BN volume fraction. At the same time, controlled size void inclusions are generated within composite assemblies in order to evaluate the IRT ability to detect bonded defects inside BN-based adhesives. It is demonstrated that thermal data post-processing methods such as Singular Values Decomposition (SVD) and Principal Component Thermography (PCT) help to get the best trade-off between mechanical performance and defect detection.

Interface crack model using finite fracture mechanics applied to the double pull-push shear test

An analytical procedure predicting a debond (interface crack) onset and growth in an adhesive joint between two beams or plates is developed and applied to a specific configuration often used in reinforcement tests in civil engineering. The procedure is based on Timoshenko beam theory and Linear Elastic-(Perfectly) Brittle Interface Model (LEBIM) combined with the Coupled Criterion of the Finite Fracture Mechanics (CC-FFM) for mixed-mode fracture. First, a sixth order differential equation in the shear stresses along the adhesive layer is deduced and solved, leading to closed form expressions for both shear and normal stresses in the adhesive. Then, the critical value of the applied load necessary to produce debonding is predicted by coupling a stress and an energy condition based on: (i) the stress distribution produced in the interface before the debond onset and (ii) the energy released during the debonding process along the interface. Although the developed procedure can be applied to several types of joints with different geometries, materials and loads (e.g., double lap joint tests including adherents made of steel or composites), herein it is applied to the double pull-push shear test where the debond onset and growth between a Carbon Fibre Reinforced Polymer (CFRP) laminate and a concrete block occurs. For such a case, the debond is produced under predominant fracture mode II; nevertheless, it is shown that relevant normal (peeling) stresses associated to mode I may appear as well. A comparison of the present solution with a previous one by the shear-lag model is provided as well.

Influence of curing conditions on mechanical behaviour of glued joints of carbon fibre-reinforced polymer composite/concrete

Polymeric adhesivesare widely used for the bonding of carbon fibre-reinforced polymers (FRPs) on a concrete structure. Structural reinforcement using FRPs is a very efficient strategy owing to the good mechanical characteristics of FRPs and the implementation methods, which are applied onsite and make it possible to reduce the work time. Efficiency is limited by FRP debonding and adhesive has a key issue to play in the strengthening. Working onsite assumes that the conditions for implementation are highly dependent on the climate. In this context, it should be noted that the resins used are cold-curing epoxy and that their mechanical and physical properties are temperature- and humidity-dependent. In this study, the impact of the application temperature on the behaviour of composite reinforcement is investigated. The objective is to analyse the mechanical and physical behaviour of epoxy polymers used for reinforcement by measuring the mechanical properties of composite adhesion on a concrete support via double-shear and pull-out tests, as well as the glass transition temperatures Tg. The Tg measurements are performed using differential scanning calorimetry and thermomechanical analysis. Double-shear tests are performed to establish the local composite-to-concrete shear laws for adhesive joints according to the nature of the polymers and the curing conditions. The test results allow for determination of the bonding length (Le) and its dependence on the curing conditions. The physical measurements of Tg support the study by elucidating the influence of the curing conditions on these properties.