Adhesive Connections Research Articles

A novel triaxial failure model for adhesive connections in structural glass applications

Structural adhesive connections for glass applications have been widely investigated in the past years, because of their enhanced mechanical performance when compared to bolted connections. However, due to the lack of established design methods and failure criteria, laboratory tests must always be performed, when adhesive connections are used in real-world structural applications. Because of the above, this work presents the analytical development of a Generalized Triaxial Model (here called GTM) that describes a novel failure criterion for adhesive materials in structural glass applications. This is done developing a generalized triaxial model defined over the three-dimensional stress space, which accounts for the non-linear effects of strain rate and temperature variation. The main output of this work is a five-dimensional formulation that allows to account for a generic stress state by a governing equation expressed as a function of the three-dimensional stress tensor. Both deviatoric and hydrostatic energetic components are taken into consideration by means of a non-linear function of the two contributions. The governing equation is represented in the stress space by a revolution surface that is axial-symmetric with respect to the hydrostatic axis, thus independent of the third stress invariant. The proposed model is suitable for isotropic materials and it is here applied to SentryGlas and TSSA, two adhesive materials used in structural glass applications, for which extensive test campaigns have been performed but for which no failure criteria are available yet in literature. Firstly, the proposed model is analytically compared to other existing general failure criteria. It is shown that some of the existing models that can be found in literature can be seen as a particular case of the proposed model. Then, the model is compared with the experimental results under different loading conditions, strain rates and temperatures. The results are found to be in line with the model predictions for both materials. Additional tensile-torsion tests are also performed to validate the proposed model at varying values of the hydrostatic angle.

Assessing the Tensile Capacity of Cold-Formed Steel Connections using Self-Drilling Screws and Adhesive Materials

This paper presents a review of the proposed design for assessing the tensile capacity of a simply truss framing system of cold-formed steel. A series of connection tests were made to investigate the capacity of connections by its deformation and load caring capacity. Furthermore, Screw connections were compared to adhesive connections. Those were created of 1 screw to 3 installed screw using 8 mm screw. On the other hand, 50%, 75% and 100% percentage of adhesive, i.e., A3M and ASK were also added to be evaluated. As a result, the experimental condition was carried out for developing a model to predict the performance capacity of each specimen. The test specimens are a single lap C connection with one end fixed by a grip, and the other end is tensioned. Each specimen was subjected to the load maximum capacity and the load deformation behaviour. The adhesive material was made of the total area of screw connection which is controlled by the volume of its area. Further, the comparison connection was considered for the analysis of the connection capacity, which was estimated from the specimen’s maximum load and the load-deformation behaviour. This research is also considered to face the problem of significant fracture mechanism and used as a further alternative solution. As a result, both adhesive materials could easily displace screw connection. ASK has a lower strength capacity than A3M but implied a better fracture mechanism. It was offered nearly similar behaviour and was suggested to evaluate the behaviour of screw-adhesive connection in advance.

Influence of artificial aging on structural adhesive connections for façade applications

Contemporary architecture often requires adhesive connections as a bonding method of façade cladding elements to the supporting substructure, due to their visually smooth surface without the interruption by bolts. Low strength, elastic and durable silicone sealants have been used in façades for a long period of time, but there is a lack of information about semi-flexible and semi-rigid adhesives with higher strengths. The building façade is a very specific application for adhesive connections due to the requirements for durability, strict geometrical imperfections and joining of unconventional materials often used in the façade design. The presented paper is focused on experimental analyses of structural adhesive joints exposed to laboratory aging conditions. Due to the absence of a particular code intended for structural adhesive joints in façades, two artificial aging procedures were chosen – ETAG 002 and ISO 9142 - E4 Procedure (Exposure to neutral salt spray and elevated temperature and humidity). The joints are bonded by two different adhesives, Silane Terminated Polymer (STP), and a two-part acrylate adhesive. The joints are composed of blank aluminum with a smooth and roughened surface, anodized aluminum and galvanized steel with a smooth and roughened surface. Mechanical behavior and failure modes of a reference set of specimens are compared with the results of two specimen sets exposed to aging. The degrading effect of demineralized water immersion was more crucial for the STP adhesive than the salt spray test. On the contrary, the effect of the salt spray test was more serious for the acrylate adhesive than immersion in water. The experimental study showed that the degrading effect of a particular aging procedure can be more harmful to one adhesive than the others in dependence on the time of exposure.

Failure Monitoring and Condition Assessment of Steel-Concrete Adhesive Connection Using Ultrasonic Waves

Adhesive bonding is increasingly being incorporated into civil engineering applications. Recently, the use of structural adhesives in steel-concrete composite systems is of particular interest. The aim of the study is an experimental investigation of the damage assessment of the connection between steel and concrete during mechanical degradation. Nine specimens consisted of a concrete cube and two adhesively bonded steel plates were examined. The inspection was based on the ultrasound monitoring during push-out tests. Ultrasonic waves were excited and registered by means of piezoelectric transducers every two seconds until the specimen failure. To determine the slip between the steel and concrete a photogrammetric method was applied. The procedure of damage evaluation is based on the monitoring of the changes in the amplitude and phase shift of signals measured during subsequent phases of degradation. To quantify discrepancies between the reference signal and other registered signals, the Sprague and Gears metric was applied. The results showed the possibilities and limitations of the proposed approach in diagnostics of adhesive connections between steel and concrete depending on the failure modes.

Assembly force modelling method on fixtures of automotive body compliant sheet metal parts

Some assembly forces will be generated on fixtures because of some existing variation sources during the welding process of automotive body compliant metal parts. This article proposes an assembly force modelling method on fixtures during the welding process of compliant sheet metal parts to decrease the assembly forces. The assembly force models on fixtures are established to show the influence relationship between assembly forces and all variation sources, and the finite element method is used to obtain all influence coefficients of assembly forces. The obtained assembly force models on fixtures describe the propagating principle of assembly forces in all welding subprocesses. Cases of different fixture layouts show that the fixture layout can greatly influence assembly forces on fixtures. So assembly forces on fixtures can be decreased through the optimization of variation sources and the fixture layout. This method can also be referred for other assembly processes, such as adhesive connection and fastener connection of compliant sheet metal parts.

Transparency in Structural Glass Systems Via Mechanical, Adhesive, and Laminated Connections ‐ Existing Research and Developments

The consistent architectural transparency demand in buildings is highly promoting the structural use of glass, in combination or to replace load‐bearing components made of traditional constructional materials. Despite its huge application in facades, roofs, envelopes, frame components, however, glass still represents a rather innovative and not well‐known material, requiring specific design conceptsm and further extended studies, toward the fulfillme nt of safe design requirements. A key role in glass systems and assemblies involving multiple components is given to connections. Major issues in their design, consequently, arise from restraining single glazing elements, as well as from ensuring their mechanical interaction with other constructional systems, as a part of full 3D buildings, including several materials, and various loading/boundary conditions. In this paper, an overview of typical connection types in use for glass systems is presented, with special consideration for mechanical, adhesive, and laminated adhesive connections, giving evidence of their typical applications, evolution, current design issues. Existing research and major projects are also discussed, both at the material/component level as well as at the assembly level.

Experimental and numerical analysis of thick embedded laminated glass connections

Laminated glass components are usually realized by bonding glass plates using interlayer polymers that develop adhesion forces during lamination. Recently, these adhesion forces have been used also to realize special adhesive connections for structural glass components and assemblies. The typical example of such a joining technique is conventionally known as “embedded laminated connection”, where a metal insert is encapsulated in multi-ply laminated glass components.In this study, careful consideration is paid for the investigation of the mechanical behaviour of embedded laminated connections with thick metal insert. To this aim, small-scale laboratory tests, Finite Element (FE) numerical models and analytical considerations are presented. Firstly, the results of experimental investigations at different temperatures are discussed, giving evidence of the geometrical and mechanical parameter effects on the so observed performances. It is observed, in particular, that the temperature affects not only the maximum load carrying capacity but also the failure mode of the studied connection typology. Non-linear numerical simulations are then developed in ABAQUS on FE models, able to account for the geometrical and mechanical properties of the reference connection specimens. Further analytical considerations are also presented, in support of the observed experimental findings. It is shown, in particular, that as far as high temperatures are not attained, the mechanical performance and failure mode of the examined connections is strictly related to glass breakage. In addition, it is also observed that at high temperature, failure mode (i.e. bubble formation) and failure location are in line with the expectations. Rather close correlation can be also found for the same embedded connections between test results, FE numerical simulations and analytical assumptions.

A study on Cold-formed Steel Frame Connection: A review

This paper is aimed to review the current researches on Cold-formed steel (CFS) structures, particularly for screw connections, welded connections, bolted connections and adhesive connections. Connection presents as a major parameter of the important elements for CFS framing system in order to attain its structural stability. The performance of different CFS connections is well-discussed in order to capture the behaviour of each type of connection. Based on the review assessment, the results highlighted that all types of connections except adhesive connections have shown the proper behaviour that can trigger the change of any design codes. Otherwise, adhesive connection is given several advantages that leads a novelty in the construction technology. Hence it still has some gaps of knowledge that are needed to be filled with comprehensive future researches.

Shear properties evaluation of a truss core of sandwich beams

The open-cell cores of sandwich structures are locally bonded to the face layers by means of adhesive resin. The sandwich structures composed of different parent materials such as carbon fibre composites (laminated face layers) and metallic core (aluminium truss core) brings the need to closely analyse their adhesive connections which strength is dominated by the shear stress. The presented work considers sandwich beams subjected to the static tests in the 3-point bending with the purpose of estimation of shear properties of the truss core. The main concern is dedicated to the out-of plane shear modulus and ultimate shear stress of the aluminium truss core. The loading of the beam is provided by a static machine. For the all beams the force - deflection history is extracted by means of non-contact optical deflection measurement using PONTOS system. The mode of failure is identified for each beam with the corresponding applied force. A flexural rigidity of the sandwich beams is also discussed based on force - displacement plots.

Glass fins with embedded titanium inserts for the façades of the new Medical School of Montpellier

The new Medical School of Montpellier, designed by Francois Fontes, is enclosed by several facades stiffened by the use of glass fins up to 12.71 m high. The main facade assures the monumentality of the institution with its length of more than 60 m. The facade glass panels, with a maximum size of $$3.8\times 2.8$$ m, are stacked transferring the dead load to the bottom panels through plastic setting blocks. The facade panels are fixed with patch-fittings bolted to titanium inserts embedded in the vertical glass fins. The structural system is designed to resist seismic actions and to accommodate the displacement of the main structure under an earthquake scenario. The stability to lateral buckling and under seismic loads is guaranteed by a system of cables and rods which transmits the in-plane forces to the main structure. The post-breakage behaviour of the multilaminate heat-strengthened glass panels and the design of the facade guarantee the stability even under very aggressive accidental scenarios. The paper contains the main issues about the fabrication of titanium inserts laminated with SentryGlas® interlayer. The verification methodology of the glass fin with embedded titanium connections in terms of strength and stability is described. In particular, non-linear buckling analysis and stability checks based on Eurocodes are proposed. The numerical analyses were completed with pull-out tests of aged specimens in order to determine the resistance of the adhesive connections. Finally, a full-scale glass fin was submitted to a three-point bending test to validate the design including the post-breakage behaviour. A brief description of the construction phase is also included.

Laminated connections under tensile load at different temperatures and strain rates

In the last years, a novel typology of adhesive connections for structural glass application has emerged, known as laminated adhesive connections, which makes use of the transparent ionomer SentryGlas® (SG) from Kuraray and the Transparent Structural Silicon Adhesive (TSSA) from Dow Corning. Despite being used in several projects, limited information is available in literature on their mechanical behaviour and on the effects of strain rate and temperature. In this work the behaviour of laminated connections under tensile loading is studied by means of experimental, analytical and numerical analyses. The experimental investigations show that temperature and strain rate variations have important effects on the mechanical response of the connections. Two main interesting phenomena are also observed: the whitening phenomenon in TSSA and the development of bubble within the SG adhesive. The analytical studies of the stress state show that confinement state of the adhesive induces a non-uniform three-dimensional stress distribution in the adhesive with a dominant hydrostatic component of the stress tensor, which is observed to be in agreement with the experimental results. Three-dimensional finite numerical analyses show that the stress field deviates from the uniform distribution with a large gradient of hydrostatic and deviatoric stresses over the adhesive area. The output of the finite numerical model are then compared with the observations of the experimental campaigns. Herein, the full set of numerical results is synthetized by the definition of so-called stress factors. The latter allow to derive the three-dimensional stress state in the adhesive at different temperatures and to compute the stress peak in the non-linear stress field distribution. Finally, prediction models are proposed for the tensile resistance of TSSA and SG laminated connections. A logarithmic law is proposed for the strain rate effects for both TSSA and SG connections. Linear and inverse hyperbolic-tangent-based laws are instead proposed for the TSSA and SG temperature effects, respectively.

Adhesive connections in glass structures—part I: experiments and analytics on thin structural silicone

The present paper describes different types of experimental test setups to determine material properties of thin structural silicone used as laminated connections in glass structures. Since it is of major interest to conduct homogeneous experiments with structural silicones, which belong to the family of rubber-like materials, the triaxiality will be introduced, which allows one to illustrate differences between homogeneous and inhomogeneous experiments. With the help of this scalar, it is possible to design experimental test setups, which ensure a homogeneous stress and strain distribution within the tested rubber-like material. Furthermore an engineering approach to determine the testing speed of arbitrary experiments dependent on one reference testing speed and experiment will be presented. This approach ensures equivalent strain energies between arbitrary and reference test specimens during testing, by which expensive strain rate controlled experiments can be relinquished, since rubber-like materials exhibit a strain rate dependency. Based on this, homogeneous experimental tests were conducted: uniaxial tension and compression, biaxial tension as well as shear-pancake tests. Furthermore, microindentation tests as inhomogeneous tests were performed. Afterwards the experimental results were processed in a manner that it is possible to identify hyperelastic material parameters via standard fitting routines as well as inverse methods, which will be presented in part II of this publication.

Subcomponent development for sandwich composite wind turbine blade bonded joints analysis

In the sector of wind energy, the trend to increasing turbine size is ongoing and it will continue to do so. This research focuses explicitly on a particular aspect of structural design which is reported to be very critical in many designs of wind turbine blade wing box structures, namely the connection between the spar web and the spar cap, which are usually built up with sandwich materials. A pyramid structured approach is developed which links local phenomena of stress transfer and failure in the adhesive connection to overall loads on the entire machine. This paper focuses on the subcomponent level of the pyramid scheme and it shows the relevance of investigations and experiments on this level. A specific test structure is designed and manufactured as a C-beam to reproduce load transfer phenomena as they occur in real blades. An experimental test campaign is conducted using different data acquisition principles and sensors to monitor structural behaviour. Results from a finite element model are compared to experimental results and satisfactory results are obtained.

Study of hybrid dryer prototype and its application in pregerminated rough rice drying

ABSTRACTIn this study, a hybrid dyer, combining heat pump drying (HPD) with fluidized bed drying (FBD) concepts were designed and fabricated. The pregerminated rough rice (pre-GRR) was dried in multistage using this hybrid dryer to compare with the single-stage drying by hot air dryer. The objectives were to test the application of this hybrid dryer and determine the suitable drying condition for pre-GRR. The result indicated that the punched plate distributor was the most suitable distributor. The pre-GRR should be dried by the three-stage drying method using either FBD or HPD at 45°C in the last stage to obtain higher head rice yield, lower fissure grain, and better color values than their counterparts. The scanning electron micrographs proved that starch gelatinization occurred when applying FBD at temperatures between 100 and 140°C causing the adhesive connections inside the kernels and subsequent decrease in fissures.

Hemicellulose extraction and characterization for applications in paper coatings and adhesives

Hemicellulose materials are arguably the second most abundant renewable component of lignocellulosic biomass after cellulose. They are relatively under-utilized hetero-polysaccharides present in lignocellulosic biomass. In this research an alkaline treatment was optimized for extraction of polymeric hemicellulose from fully bleached hardwood pulp (B-HWP) and partially delignified switchgrass (SWG). The hemicellulose extracted from B-HWP was relatively pure with zero percent lignin and 89.5% xylose content whereas the partially delignified SWG hemicellulose contained about 6-3% lignin and 72–82% xylose, depending on the NaOH concentration during extraction (3–17% NaOH solution). A maximum molecular weight of SWG hemicellulose of 64,300g/mol was achieved for the 10% NaOH solution extraction, whereas the MW of B-HWP hemicellulose at 10% NaOH solution extraction was lower at 49,200g/mol. We have demonstrated that the residual lignin in SWG hemicellulose lowered the system Tg and this might be utilized as a way to increase the applications of hemicellulose in high value biomaterials. Furthermore, the hemicellulose could be crosslinked with zirconium to develop a water resistant gel for coating or adhesive applications. Our results showed that the loading stress required to break an hemicellulose based adhesive connection between two paper surfaces was 0.89, 2.02, 2.75, 3.46, and 3.11 (MPa) for 2, 4, 6, 8 and 10% AZC samples, indicating that up to about 8% AZC crosslinker in the hemicellulose increases the adhesive behavior of the material.

Experimental and numerical evaluation of the axial stiffness of the web-to-flange adhesive connections in composite I-beams

In most full-composite structures nowadays, pultruded profiles are joined together to form more complex cross-sections that are not produced by the pultrusion process. These unconventional cross-sections represent a critical point in terms of strength and deformability of the whole structure, especially due to the presence of adhesive. This fundamental unknown aspect recently inspired the authors of the present paper to study the mechanical behavior of a glass fiber reinforced polymer (GFRP) profile with a complex cross-section shape obtained by bonding simple pultruded plates (bonded beams) by epoxy resin. The first step was to compare the behaviors of bonded beams with those of similar pultruded ones. With this aim, in a previous paper the flexural global behavior of an I-bonded beam was investigated, highlighting its better performance with respect to the pultruded I-profile in terms of failure load and stiffness. Now the authors would like to extend the study, both experimentally and numerically, to the mechanical behavior of the adhesive web–flange connections in terms of axial stiffness.Seventeen full specimens were tested by performing pull-out tests under force control. A uniformly distributed load was applied to the lower flange in order to favor the detachment of the flange from the web of the profile by using a steel device designed and realized ad hoc.The overall result of the research is that the bonded profile shows a good mechanical behavior justifying its use in technical practice. In addition, the bonded beams represents a valid alternative to the pultruded profile especially when the latter is not available on the market. In more detail, in bonded beams, the presence of the resin (instead of resin and fibers as in pultruded beams) at the web-to-flange connection does not affect the flexural global behavior but does penalize the axial behavior of their connections, as here demonstrated.

CEO Tenure, Market Competition, and Sticky Pay‐without‐performance as the Extraction of Rents

AbstractThis study examines the undesirable impact of CEO tenure on downwardly sticky pay, and the moderating effect of higher market competition on the potential adhesive connection between CEO tenure and sticky pay. We find that CEO pay stickiness intensifies as CEO tenure increases. This suggests that entrenched executives extract greater levels of baseline rents through strong exclusivity. In contrast, we find that in firms with long‐tenured CEOs, higher levels of competition intensity alleviate CEO pay stickiness. These results imply that although long‐tenured CEOs tend to exert a powerful influence over the pay‐setting process, increased competition restrains CEOs’ rent‐seeking behavior.

Experimental investigation of novel pre-tightened teeth connection technique for composite tube

A new composite tube connection method called the pre-tightened teeth connection technique is proposed to improve the composite tube connection efficiency. This paper first introduces the manufacturing process of the proposed technique. It then outlines how the mechanical properties of this technology were tested using four test groups. The factors that influence the load-bearing capacity and damage model of the connection were analyzed, and finally, the transfer load mechanism was investigated. The following conclusions can be obtained from the research results. (1) The new technique improves the compressive connection efficiency by a maximum of 79%, with the efficiency exceeding that of adhesive connections of the same thickness. (2) Changing the depth of teeth results in two types of damage: local compressive damage and shear damage. The bearing capacity can be improved by increasing the depth, length, and number of teeth as well as the pretightening force. (3) The capacity of the technique to transfer high loads is a result of both the relatively high interlaminar shear strength of the pultruded composite and the interlaminar shear strength increase provided by the pre-tightening force. The proposed technique shows favorable mechanical properties, and therefore, it can be extensively applied in the engineering field.

Guided wave propagation for assessment of adhesive bonding between steel and concrete

Adhesive bonding is becoming more increasingly important in joining of structural elements. In civil engineering, there is a growing interest in connection by adhesive bonding in steel-concrete flexural members. This study concerns the guided wave propagation technique applied to condition assessment of an adhesive connection between a steel member and a concrete beam. Various states of degradation were considered by producing several laboratory samples differing in the placement and the length of the adhesive bond. Piezoelectric transducers were used to excite and to register signals of propagating waves. In addition, the finite elements method was used to simulate propagation of guided waves at the bond-line between steel and concrete. Results for the beam with perfect bonding were compared with results obtained for beams with partially degraded connections. The influence of the length of damaged bond and its position on registered signals was investigated.

Study on Tensile Mechanical Behavior of Composite T-Joints

Based on three kinds of composite T-joints with different connection way for tension test outside the plane, it was obtained contrastively that how the ordinary adhesive, Z-pin reinforcement and stitching reinforcement three different fitting influence tensile strength, damage failure process and failure mode of composite T-joints. The test results showed that compared with ordinary adhesive connection mode, tensile strength of the Z-pin reinforcement and stitching reinforcement T-joints increased by 13.6% and 11.4%, respectively; and the largest deformation increased by 19.2% and 15.1%, respectively. After reaching maximum load condition, the ordinary adhesive T-joints had brittle failures, but Z-pin reinforcement and stitching reinforcement T-joints all showed that the ductile damage behavior, corresponding to the load-displacement curve appeared saw-tooth wave platform. Obviously, the Z-pin reinforcement T-joints had the most significant reinforcement effect on tensile properties of composite laminates T-joints.