Joining of composite materials has been an issue ever since composites were introduced. Among various joining methods, adhesive joining has been widely adopted because the adhesive joining uniformly ...distributes stresses over larger area, while the mechanical joining of composites induces stress concentration and fiber breakout. However, adhesive joining requires the surface treatment of composite adherends to increase the bonding strength; this treatment is not only costly but also generates much environmental pollution.
In this study, a composite adherend that does not require any surface treatment to constitute an adhesive joint is developed. The composite adherends are manufactured by a “soft layer method” to expose bare fibers on the surface during composite fabrication. The bonding strength was significantly improved due to the exposed bare fibers, which was comparable to that of the adhesive joint treated by the conventional peel ply method without generating waste materials.
In this paper, the connection stiffness between a thin-walled Z-beam and a sandwich panel is investigated by means of laboratory experiment, analytical approach, and numerical simulation. The scheme ...of the conducted experiment refers to a double lap shear test. The two thicknesses of the sandwich panel (100 mm and 60 mm) and two groups of fasteners (four and three) were investigated. The laboratory tests allowed for the determination of the failure mechanisms and the prediction of the reliability of the restraint of the thin-walled beam, provided by sandwich panels. The assumed finite element model created in Abaqus/CAE consisted of solid finite elements (core layer of the sandwich panel, roller support) and shell finite elements (thin-walled beam, facings of the sandwich panel). The fasteners were modeled implicitly, i.e. using spring connectors. The stiffness of the spring connector was determined on the basis of the derived analytical expression and the laboratory test results. The kinematical response of the adopted finite element model was in agreement with the laboratory results. Such a model can be used to verify more complex finite element models with explicitly introduced fasteners.
ABSTRACT
Intensive studies of polymer adhesives for structural applications have opened up new possibilities of glued usage connections in civil engineering, especially in façade applications. ...Facades have to fulfil not only architectural requirements but there are also construction and material technology requirements, as well as functionality. Façade cladding connections with other façade parts can be advantageously designed as glued joints. In dependence on particular application, adhesive bonding provides higher efficiency of workmanship in comparison with bolted connection and esthetical qualities, e.g. smooth, flat surface of façade cladding without visual interruption of bolts. Important benefit of glued connections in facades is elimination of local thermal bridge in comparison with bolted connections and possibility of stress peak reduction in dependence on adhesive and substrate stiffness and geometrical arrangement of the joint. Despite of wide usage of low strength and elastic silicone sealants for a long period of time in façades, there is a lack of information about semi‐flexible and semi‐rigid adhesives with higher strength and reasonable elongation at break. Building facade is a very specific type of usage for glued connections due to the requirements on durability, strict geometrical imperfections and joining of unconventional materials often used in the façade design. This paper reports on an experimental analysis focused on determining of the mechanical characteristics of two types of adhesive applied in double lap connection loaded by shear. The study comprises two basic substrate materials, aluminium and galvanised steel, with various surface treatments. Galvanized steel was used with clean, smooth surface and roughened surface; aluminium substrates were applied with clean smooth surface, roughened surface and with anodised covering to find out effect of roughening and anodization of aluminium on adhesion. Material and surface treatment has great influence not only on adhesion and thus strength of the joint, but also on failure mode, behaviour and safety of particular joint. Moreover, every necessary surface treatment creates higher labour intensity, higher time consumption and thus increased costs on building/facade construction.
Bond behavior between concrete, which has been cracked by alkali-silica reaction (ASR), and fiber-reinforced concrete polymer (CFRP) sheets is investigated with double-lap shear specimens, assembled ...using concrete blocks (150x200 × 150 mm3) and CFRP sheets at various bond lengths and widths. The blocks were cast with reactive silica particles before being treated in a sodium hydride solution to accelerate ASR; others were prepared using non-reactive particles and kept in lime water as controls. Empirical models were developed to predict bond force based on the present data. Results show significant reductions in the ultimate bond force (reaching about 69%) as ASR progresses.
•Bond characteristics between CFRP and concrete were determinately affected by ASR.•Dimensions of CFRP sheets affected the percentage reduction in bond due to ASR.•Bond models developed showed higher precision as compared to those in literature.
This paper investigates the creep behavior of adhesively bonded concrete/fiber-reinforced polymer (FRP) joints, through experimental and modeling approaches. The first part proposes a methodology for ...predicting the long-term creep response of the bulk epoxy adhesive; such a procedure consists of (1) performing short-term tensile creep experiments at various temperatures and stress levels, (2) building the creep compliance master curves according to the time-temperature superposition principle in order to assess the long-term evolution for each stress level, and (3) developing a rheological model whose parameters are identified by fitting the previous master curves. In our case, it was found that master curves (and, consequently, parameters of the rheological model) are dependent on the applied stress level, highlighting the nonlinear creep behavior of the bulk epoxy adhesive. Therefore, evolution laws of the model parameters were established to account for this stress dependence. The second part focuses on the creep response of the concrete/FRP assembly in the framework of a double lap joint shear test configuration. Experiments showed that creep of the adhesive layer leads to a progressive evolution of the strain profile along the lap joint, after only one month of sustained load at 30% of the ultimate strength. Besides, a finite element approach involving the abovementioned rheological model was used to predict the nonlinear creep behavior of the bonded assembly. It confirmed that creep modifies the stress distribution along the lap joint, especially the stress value at the loaded end, and leads to a slight increase in the effective load transfer length. This result is of paramount interest since the transfer length is a key parameter in the design of FRP-bonded strengthening systems. Moreover, instantaneous and long-term calculated strain profiles were found in fair agreement with experimental data, validating the modeling approach.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A trend towards adhesive connections instead of mechanical ones can be observed for transparent facades in recent years. Furthermore, research efforts are made to increase the efficiency regarding ...material use by designing systems with composite structural behavior. In this article, experimental and numerical results obtained for linear structural silicone joints between glass and stainless steel substrates, investigated separately under tensile and under shear loading, are discussed. The two selected adhesives, Dow Corning® 993 and Sikasil® SG-550, are approved for structural sealant glazing systems and are planned to be used within a novel concept for façade elements with composite structural behavior, consisting of a glass pane and a filigree metal framing. For an adhesive joint with prismatic geometry, the influence of different lengths, widths and thicknesses of the joint on its mechanical performance is assessed experimentally under tensile loading, while under shear loading only different thicknesses are investigated. Both under tensile and under shear loading, a dependency of the failure engineering stresses on the joint thickness is noticed. In a second step, the suitability of selected hyperelastic models is assessed for predicting the load versus displacement behavior of the investigated linear adhesive joints. The parameters required for these models are determined based on uniaxial tensile tests on dumbbell specimens.
Structural adhesive bonding is very often used joining method in aerospace and automotive industry, but in civil engineering, especially in façade applications, semi-flexible or semi-rigid adhesives ...are still rarely used. The article is focused on experimental analyses of structural adhesive joints intended for façade applications (e.g. bonding of façade cladding elements to the supporting substructure). The experimental study contains a comparison of the structural behavior of two different adhesives in joints with aluminum or zinc-electroplated steel substrates with various surface pre-treatments. The main goal of the study is a comparison of the mechanical properties of joints exposed and unexposed to laboratory ageing conditions; immersion on demineralized water according to ETAG 002 (Guideline for European Technical Approval for Structural Sealant Glazing Kits). Water content in adhesive layer can change significantly its mechanical properties and adhesion of glue to the substrate. Ageing resistance of joint can be improved by durability increasing of the substrate. For this reason, two different substrate materials with various surface treatments (mechanical roughening, smooth surface, anodizing) were tested. Different adhesive resistance against humid conditions was observed depending on the substrate material and pre-treatment. STP polymer joints showed strength reduction by 30% after immersion for almost all substrates, while acrylate adhesive proved 20% strength reduction for roughened aluminum substrate and 60% strength reduction for zinc-electroplated steel substrate with a roughened surface. The zinc-electroplated steel substrate showed problematic adhesion in case of the acrylate adhesive both reference set of specimens and specimens exposed to laboratory ageing. The positive effect of roughening on adhesion and ageing resistance was clearly observed in the specimens bonded by the acrylate adhesive.
The main aim of paper is to conduct finite element analysis of sandwich composites under different loadings. Sandwich composites of Glass fabric reinforced Epoxy skins and Rigid Poly Urethane ...FoamCore of three different densities are tested under three-point bending setup to obtain the flexural properties, Foam cores are tested under tension and compression to evaluate their axial behavior. Sandwich specimens are tested in T-Peel, Single Lap Shear and Double Lap shear to evaluate their shear behavior under tensile loading and to observe mode-I, mixed mode, and mode-II failure of specimens.Forall ofthe above tests Finite Element Analysis(FEA) is carried out using ANSYS™ and experimental and FEM values are verified. In three-point Bending test Sandwich beams are fabricated and tested with different skin to core weight ratios and different span to depth ratios and while testing different failure modes are observed. These Failure modes are correlated with FEM and failure criteria are applied as per failure and all the obtained values are compared.
The influence of imperfect bonding, owing to partial lack of adhesive, on the strength of composite non-crimp fabric (NCF) double-lap shear (DLS) joints was experimentally and numerically ...investigated. Fabrics were layered and compacted using a thermoplastic veil while infiltration of the preforms was done using the vacuum assisted process. Paste adhesive bonding was carried out by implementing the novel insertion squeeze flow process. Quality of adhesive bonding was tested using X-ray imaging and ultrasonic C-scan inspection. The tensile lap shear strength of the DLS joints was determined experimentally. Digital macrographs revealed that the specimens failed due to shear failure of the adhesive (debonding) and fracture of the composite boundary layer. As a second approach, a mesomechanical model based on the FE method and the (homogenized) progressive failure analysis method was developed. In the model, the areas without adhesion, as detected by the C-scans, were included. Numerical simulations of failure initiation and progression at the NCF joint and the adhesive indicated that it is possible to predict the strength and failure mechanisms of the imperfect bonded DLS joints.
The present work focuses on simulation of nonlinear mechanical behaviors of adhesively bonded DLS (double lap shear) joints for variable extension rates and temperatures using the implicit ABAQUS ...solver. Load–displacement curves of DLS joints at nine combinations of extension rates and environmental temperatures are initially obtained by conducting tensile tests in a UTM. The joint specimens are made from dual phase (DP) steel coupons bonded with a rubber-toughened adhesive. It is shown that the shell–solid model of a DLS joint, in which substrates are modeled with shell elements and adhesive with solid elements, can effectively predict the mechanical behavior of the joint. Exponent Drucker-Prager or Von Mises yield criterion together with nonlinear isotropic hardening is used for the simulation of DLS joint tests. It has been found that at a low temperature (−20°C), both Von Mises and exponent Drucker-Prager criteria give close prediction of experimental load–extension curves. However, at a high temperature (82°C), Von Mises condition tends to yield a perceptibly softer joint behavior, while the corresponding response obtained using exponent Drucker-Prager criterion is much closer to the experimental load–displacement curve.
