Perfect Bond Research Articles

A lined hole in a viscoelastic rock under biaxial far-field stress

In this paper, we revisit the problem of an infinite, homogeneous, isotropic, linear viscoelastic medium containing a lined circular hole in the general setting of a biaxial far-field stress and for a variety of viscoelastic models for the medium and the lining. The goal is to provide reliable ready-to-use tool to analyze the plane-strain problem of a borehole in viscoelastic rock for any type of viscoelastic model that can be expressed in differential form. The lining is modeled as an isotropic viscoelastic ring. A constant biaxial loading is applied at infinity and/or a time-dependent pressure is prescribed at the inner boundary of the lining. Two distinct scenarios are considered: (i) the hole is excavated before the lining is inserted, i.e. the radius of the hole is larger than the outer radius of the ring, and (ii) the lining is set up directly and a perfect bond is assumed between the lining and the viscoelastic material. These problems are solved using the correspondence principle. The Laplace transformed stresses and displacements in both the lining and the rock are calculated. An inverse Laplace transform is then used to obtain the time domain solution. The operations of space integration and Laplace transform are performed analytically. The obtained new solution in the Laplace domain is compared with published results as well as a numerical solution by the finite element method (for the elastic transformed problem). The Laplace inversion procedure is done either analytically or numerically. For the sake of illustration, examples are given for the cases where the viscoelastic rock responds elastically in dilation and viscoelastically in shear. Five classical viscoelastic models in shear are notably considered. The accuracy of the approach for viscoelastic problems is demonstrated by comparing selected results with a few available analytical solutions for the simpler case of a hydrostatic load at infinity and an incompressible rock. We notably clarify the validity of a number of solutions described in the literature. The efficiency of the solution presented here is illustrated by several numerical examples. For reproducibility, a Mathematica script containing all the derived solutions is provided as supplementary material.

FEM study on mechanical properties of nanocomposites reinforced by defective graphene sheets

The main objective of the present study is improvement of the mechanical property estimation of epoxy nanocomposites (NCs) reinforced by defective graphene sheets (GS). For this purpose, the mechanical properties of a defect‐free GS are initially determined using FEM. Then, some well‐known defects are incorporated into the computational model to establish a realistic computational model. In addition, the finite element analyses of a NC reinforced by such defective GSs are conducted using Full Continuum and semi‐continuum FE models. In this regard, the multi‐scale method is used to model the perfect bonds between carbon atoms and the surrounding matrix. Also, the influences of the interphase layer and defective GSs on NC properties are investigated. Finally, the effects of some basic parameters such as the weight fractions and the length of GSs on the mechanical properties are examined. POLYM. COMPOS., 40:E1084–E1093, 2019. © 2018 Society of Plastics Engineers

Design and analytical modeling of magneto-electro-mechanical characteristics of a novel magneto-electro-elastic vibration-based energy harvesting system

In order to effectively design an energy harvesting system for any specific application, a model that accurately characterizes the energy harvesting parameters is needed. In the present paper a novel magneto-electro-elastic (MEE) cantilever beam has been proposed and modeled as an effective means to increase the harvested electrical power in a vibration-based energy harvesting system. The cantilever beam is composed of a linear homogeneous elastic substrate and two MEE layers with perfect bonds between their interfaces. Using the constitutive equations, Gauss's and Faraday's laws, based on the Euler–Bernoulli beam theory, the coupled magneto-electro-mechanical (MeM) differential equations are derived for a harmonic base excitation in the transversal direction with a superimposed small rotation. The resulting equations are then solved analytically to obtain the dynamic behavior as well as the harvested voltages and powers of the proposed energy harvesting system. Finally, parametric numerical studies are used to examine the effect of excitation frequency, external resistive loads, and material properties on the performance of the MEE energy harvester. The study reveals that the implementation of the coil circuit has resulted in an increase in the total useful harvested power. According to the numerical results, any increase in the Young's modulus and density of the substrate layer (across the ranges that have been studied and while the properties of the MEE layer are kept constant), increases the magnitude of the magnetoelectric harvested power in the unimorph MEE energy harvester system.

A Semi-Infinite Strip Pressed Against an Elastic Half-Plane With Frictional Slip

The subject of this investigation is the plane strain elasticity problem of a finite width semi-infinite strip with its end pressed against a half-plane of the same material with friction. From the existing integral equation solution for a perfect bond, it is shown that the length of the zone of frictional slip and the value of the slip displacement can both be inferred. It is further shown how this method allows a finite element stress analysis of a structure, obtained with the simple assumption of a perfect bond, to be used instead of the more complicated finite element structural analysis with frictional slip. Nonetheless, the results of this simpler finite element analysis can be used to infer the length of the frictional slip zone and the magnitude of the slip displacement. It is expected that this method will be valuable in the analysis of the mechanics of fretting. Damage due to fretting fatigue is initiated due to frictional slip near the edges of the interface between two connected materials. The stress analysis of structures, which includes these frictional slip zones, is considerably more complicated than it is for a perfect bond, often making it impractical to include in a comprehensive finite element model of the complete structure. Thus, the methodology used in this paper should allow the size of the frictional slip zones and the frictional slip displacements to be inferred directly from the stress analysis for a perfect bond.

Bond-slip effect in flexural behavior of GFRP RC slabs

The use of glass fiber reinforced polymer (GFRP) composite bars as internal reinforcement for concrete is rapidly increasing especially in structures exposed to aggressive environments. A proper bond mechanism between GFRP bar and concrete is essential to ensure proper functioning of such structures. The slippage between the concrete and reinforcement has usually been ignored in numerical modeling of reinforced concrete (RC) structures. In this study, the effect of the bond action in flexural behavior of GFRP RC slabs was investigated. The analysis was first performed by considering a perfect bond between the concrete and reinforcement and ignoring any slippage. Next, an experimentally obtained bond-slip relation was used to replace the unrealistic perfect bond assumption. The predicted flexural load-deflection response of the slab was compared to the experimental data. The result obtained by incorporating the bond-slip model showed a better agreement with the experimental data. Hence, considering the slippage between the GFRP and concrete may be necessary when accurate deflection estimate is required under the service condition. Additionally, it was shown that the perfect bond assumption was sufficiently safe for the design of the GFRP RC slabs.

Analytical and numerical prediction of the bending behaviour of textile reinforced concrete sandwich beams

This paper concerns the investigation of the behaviour of sandwich beams previously tested in four point bending through analytical and numerical models. Modelling is a fundamental resource to predict the mechanical response of the element and to investigate the mechanisms that act during the evolution of the test.The sandwich beams here taken into account are characterised by external textile reinforced concrete (TRC) layers and an insulation material (expanded polystyrene, EPS) able to transfer shear stresses. Bond between the layers is obtained during production thanks to an in-pressure casting technique, and no particular device is used in order to transfer shear stresses between the layers. Two beam slenderness values are taken into account.An analytical and a numerical approach have been used in order to predict the experimental behaviour: concerning the analytical approach, a model based on the Stamm and Witte sandwich theory has been developed including material non-linearity; concerning the numerical analysis, a finite element (FE) model has been built in ABAQUS including material and geometry non-linearity. The assumption of perfect bond is used in both cases.The non-linear analytical and finite element models have been validated, as a good agreement with experimental results has been achieved. The experimental identification of material parameters - TRC in tension, mortar in compression and EPS in tension, compression and shear - is crucial for the definition of proper constitutive laws for the models and is here presented and discussed. For both approaches, the assumptions of modelling TRC in bending as homogeneous and assuming perfect bond between TRC and EPS (even when behaviour becomes highly non-linear) have been proved to be reliable. Analytical and FEM results show that EPS non-linear behaviour and TRC membrane and bending behaviour govern the response. The FE analysis also highlights the mechanisms involved in specimen failure.

An experimental investigation of a new perfect bond technology for composite slabs

Steel-concrete composite slabs generally fail due to the debonding with separation of sections caused by longitudinal shear forces, regardless of the shape of the sheeting profile or the design of the embossments. This article presents an innovative full-connection bonding technology, consisting of producing bands of many small crown-shaped cuttings in the profile webs as a replacement for the embossments. The new technology has been tested on three commercial sheeting profiles. The results of the investigation show that full connection is achieved with the new system, i.e., yielding of both materials occurs without any slip, in contrast to the partial connection of traditional embossments. The longitudinal shear strengths are 1.4–7 times higher. The specimens tested include the use of conventional galvanized steel and concrete, as well as ferritic stainless steel and lightweight aggregate concrete.

A modified RBSM for simulating the failure process of RC structures

In this paper, a modified rigid body spring model (RBSM) is proposed and used to analyze the damage and failure process of reinforced concrete (RC) structures. In the proposed model, the concrete is represented by an assembly of rigid blocks connected with a uniform distribution of normal and tangential springs to simulate the macroscopic mechanical behavior of concrete. Steel bars are evenly dispersed into rigid blocks as a kind of homogeneous axial material, and an additional uniform distribution of axial and dowel springs is defined to consider the axial stiffness and dowel action of steel bars. Perfect bond between the concrete and steel bars is assumed, and tension stiffening effect of steel bars is modeled by adjusting the constitutive relationship for the tensile reinforcement. Adjacent blocks are allowed to separate at the contact interface, which makes it convenient and easy to simulate the cracking process of concrete. The failure of the springs is determined by the Mohr-Coulomb type criterion with the tension and compression caps. The effectiveness of the proposed method is confirmed by elastic analyses of a cantilever beam under different loading conditions and failure analyses of a RC beam under two-point loading.

Üç Noktalı Eğilme Altındaki Betonarme Kirişlerde Karbon Lifli Polimerin Etkin ve Ekonomik Kullanımı

Externally bonded fiber reinforced polymer (FRP) sheets are highly popular for reinforced concrete (RC) beams to improve their flexural performance. This paper presents the results of three-point bending tests on seven RC beams externally reinforced with carbon fiber reinforced polymers (CFRP) sheets. Two concrete mixes with different compressive strength values are prepared for the production of experimental beams (150x250x1500 mm). First four beams have been casted with concrete having mean compressive strengths of 25.7 MPa and the other three beams are made of concrete having a very low compressive strength of 6.8 MPa which fall within the expected range for RC buildings constructed before 1990s in Turkey. Three different strengthening schemes are used by bonding of FRP sheets 1) only to bottom surface of the beam; 2) to bottom surface and lateral side’s surfaces of 50 mm height including the tensile reinforcement and the concrete cover; and 3) in U-wrapping. Failure mechanisms and flexural behavior of the strengthened beams are evaluated on the basis of the effectiveness of different wrapping schemes. The results are compared with the recommendations of international code ACI 440.2R-08. The validity of perfect bond assumption of FRP-concrete interface and the tensile strain limits for FRP sheets are also examined.

Effect of Soil Layering on Coupled Dynamic Response and Active Length of Piles Embedded in Layered Soil Using Cone Model

Dynamic analysis of single pile embedded in two-layered soil has been performed to study the influence of layering on the frequency dependent displacement response and active length under coupled horizontal and rocking vibration. Cone model has been used to determine the dynamic stiffness coefficient of pile. The soil and pile has been assumed to behave as elastic during dynamic loading. It has been also assumed that perfect bond exists between pile surface and surrounding soil medium. The wave generated due to pile vibration transfer to the soil through soil–pile interface and propagates to the infinity. The wave propagation has been modeled with cone model and soil–pile interaction has been incorporated through beam equation. The dynamic response of the pile obtained from the analysis has been plotted against non dimensional frequency to investigate the behavior of pile under such loading condition. The horizontal displacement profile along the depth of pile has been studied for different top layer thickness and homogeneous soil. The results showed that dynamic response is very sensitive to the thickness of the top layer and its properties. The active length of pile increases with the increase in top layer thickness.

Diffusion behavior at void tip and its contributions to void shrinkage during solid-state bonding

Solid-state diffusion bonding is an advanced joining technique, which has been widely used to join similar or dissimilar materials. Generally, it is easy to observe the diffusion behavior during dissimilar bonding, but for similar bonding the diffusion behavior has yet been observed via experiments. In this study, the diffusion behavior at void tip was firstly observed during similar bonding of stainless steel. Scanning electron microscopy with energy dispersive spectroscopy was used to examine the interface characteristic and diffusion behavior. The results showed that a diffusion region was discovered at void tip. Element concentrations of diffusion region were more than those of void region, but less than those of bonded region. This behavior indicated that the diffusion was ongoing at void tip, but the perfect bond has yet formed. The diffusion region was attributed to the interface diffusion from adjacent region to void tip due to the stress gradient along bonding interface. The mass accumulation at void tip transformed the sharp void tip into smooth one at the beginning of void shrinkage, and then resulted in shorter voids.

A new experimental investigation into the effects of reinforcing mortar beams with superelastic SMA fibers on controlling and closing cracks

Abstract This study assessed the performance of short fibers made of superelastic shape memory alloy (SE SMA) to close cracks in mortar beams. Four types of fibers were considered. Five types of cement mortar beams were manufactured. Four of these specimen types included superelastic SMA fibers such that each one was made with only one type of SMA fiber as well as steel bar, and the other specimen type was made with only a steel bar. The self-crack-closing capacity of the beams was investigated by comparing deflections upon loading and unloading through studying the post-cracking behavior. Results showed that the mortar beams resist flexural force until a crack is generated. Thereafter, the flexural load is sustained by the SE SMA fibers. Spearhead (SH) fiber provides the best self-centering behavior. A good crack recovery capacity cannot be achieved because there is a lake of flag-shaped behavior as the stress induced in the fiber does not hit the upper plateau stress due to fiber slip. The beam with only a steel bar showed a better recovery ratio than other types. For flexural crack control, a perfect bond between the SE SMA short fibers and the mortar matrix is needed to generate self-centering capacity.

On the numerical modelling of bond for the failure analysis of reinforced concrete

The structural performance of reinforced concrete relies heavily on the bond between reinforcement and concrete. In nonlinear finite element analyses, bond is either modelled by merged, also called perfect bond, or coincident with slip, also called bond-slip, approaches. Here, the performance of these two approaches for the modelling of failure of reinforced concrete was investigated using a damage-plasticity constitutive model in LS-DYNA. Firstly, the influence of element size on the response of tension-stiffening analyses with the two modelling approaches was investigated. Then, the results of the two approaches were compared for plain and fibre reinforced tension stiffening and a drop weight impact test. It was shown that only the coincident with slip approach provided mesh insensitive results. However, both approaches were capable of reproducing the overall response of the experiments in the form of load and displacements satisfactorily for the meshes used.

Nonlinear three–dimensional finite–element modelling of reinforced–concrete beams: Computational challenges and experimental validation

Abstract Three–dimensional nonlinear finite–element models have been developed to investigate the loading–unloading–reloading behaviour of two reinforced–concrete beams under four–point bending using explicit dynamics in ABAQUS. The damaged–plasticity model proposed by Lubliner and collaborators was employed for the plain concrete, and elastic–perfectly plastic models were employed for the steel reinforcement. A perfect bond was assumed between the steel rebars and concrete, whereby the bond–slip behaviour, as well as damage along crack patterns, were modelled through concrete damage. The influence of the shape of the tension–softening law on the numerical load–deflection response was studied by considering bi–linear, exponential and linear post–failure stress–displacement and stress–strain relationships. The effect of modelling steel rebars with truss or beam elements was also investigated. Structured meshes of linear hexahedral elements either with incompatible modes or with reduced integration, and unstructured meshes of either linear or ‘modified’ quadratic tetrahedral elements were considered. In terms of load–deflection curves, both the structured and the unstructured meshes gave results in very good agreement with test results. In terms of crack patterns, results predicted by the structured meshes exhibited some mesh bias, which was less pronounced with the unstructured meshes. In the post–yield phase, if a geometrically nonlinear model is used, discrepancies were found when truss elements were used for steel rebars, whereas good agreement was found if the bending stiffness of the rebars is included using beam elements. This is a non–obvious result that may be important to consider when studying the progressive collapse of RC structures.

08.31: Analysis of the load transfer between materials in composite concrete encased steel columns loaded axially

ABSTRACTThe analysis of the load distribution between steel and concrete parts of the composite concrete encased I‐shaped steel columns subjected to short‐term axial load is presented. The variable parameters were: two loading conditions − load scheme I (specimens loaded through the entire cross‐section simultaneously), load scheme II (specimens loaded only through the steel profiles protruded from the top end) and concrete class (C25/30 and C40/50). Obtained in the experiment longitudinal strains of both steel and concrete were used to compute the force transferred through the steel and concrete parts of the columns. To provide a reference level for the discussion on the results the analytical solution assuming the perfect bond between steel and concrete, Hooke's law for steel and the Rüsch formula for unconfined concrete were used. The force for which the stress in steel and concrete computed using the strain readings obtained from the experiment starts to deviate from the full bond analytical model predictions can be interpreted as the force for which the loss of adhesive bond occurs. Furthermore on the basis of the equilibrium of the infinitesimal cross section of a column, method for estimating the shear stress at which the debonding occurs is shown. The analysis showed that for columns under the load scheme I composite action of steel and concrete is in effect for the entire load range regardless of the concrete class. For elements under the load scheme II the composite action of both materials is in effect only up to a specific value of the force that changes along the height of the column. Presented method can be applied to composite steel‐concrete columns under any configuration of boundary conditions subjected to axial compression. Moreover it can be used to specify the area for which the shear connectors should be provided, to validate constitutive models of shear stress – slip behaviour that can be used is FEM analysis and to analyse adhesive bond properties also in columns made of another materials, for example reinforced concrete members strengthened with FRP sheets.

On discrete element method for rebar-concrete interaction

This work discusses the input parameters of discrete element method (DEM) for defining contact element between concrete and rebar. A comprehensive study is performed from a numerical database built in this study. A targeted method of discrete element model considering key parameters of bond strength between concrete and steel bar is developed for reinforced concrete structures so that DEM is customized for defining bond-slip effect between rebar and surrounding concrete. Accuracy of hypothesis is validated by an experimental program. Results show that the targeted method of discrete element model is more applicable and precise than embedded element method in which the perfect bond with no slip is dominant between the materials.

A model for the bond-slip of a GFRP bar in concrete

Abstract Glass fiber reinforced polymer (GFRP) bars are emerging as desirable alternatives for traditional steel reinforcements in concrete industry. A proper bond between concrete and reinforcement is critical for the performance of reinforced concrete structures. Due to the complexity of modeling the bond action, a perfect bond has been usually considered with the slippage between concrete and reinforcement neglected. The purpose of the present study is to develop a parametric bond-slip model based on pull-out tests performed on sand coated GFRP bars. It included exponential rising, linear descending and residual constant bond stress stages. A sensitivity analysis was performed to determine the bond parameters. Different points along the embedded length of the bar were monitored to illustrate the difference between the average and nodal bond-slip relationships. The proposed bond model was used in a finite element analysis that modeled the cracking in concrete and explicitly simulated the bond action. The model was capable of presenting both concrete splitting and pull-through modes of failure. Simulations were performed on samples with different concrete covers to demonstrate both failure modes.

Strengthening mechanism of channel steel plate for notched concrete beams against fracture: Test and numerical study

Concrete structures are intentionally built with notches or incomplete joints in many engineering practices to deal with complex loading conditions. It is of great significance to improve the crack resistance and the installation of a channel steel plate ahead of the purpose-built notch (or joint) tip may serve such a purpose. This paper presents an investigation into the strengthening mechanism of installing a channel steel plate at the head of a notch for concrete beams against opening mode fracture failure. Both test and numerical studies have been undertaken and particular attention is given to the effects of key factors on the load carrying capacity and the failure pattern. Two types of three-point bending tests were conducted on concrete beams with or without channel steel plate reinforcement for a comparison study. The test results demonstrated the capability of channel steel plate measure for increasing the beam load capacity, and the interface debonding and matrix cracking were responsible for the eventual failure of reinforced concrete beams. Correspondingly, finite element based numerical models were established to investigate the progressive cracking in test beams and the strengthening mechanism by the installation of a steel plate. A damage-plasticity material model was used for simulating the cracking development in concrete, whilst two different approaches were adopted for the steel-concrete interface modelling: one assumed a perfect bond while the other incorporated a discrete thin layer of interface to allow for potential debonding and slippage. A comparison between the numerical and test results was given, and the effects of key factors on the performance of beams with steel plate measure were investigated through parametric numerical studies. The paper ends with some discussions on the strengthening mechanism and conclusions.

Nonlinear Finite Element Analysis of FRP Strengthened RC Beams with Bond-Slip Effect

This paper investigates the structural behavior of fiber reinforced polymer (FRP) strengthened reinforced concrete (RC) beams by developing a new simple, efficient and accurate finite element model (FEM-B). In addition to the FRP, concrete and steel rebars, the adhesive and stirrups which have been generally ignored in the reported models from literatures are considered in the new models. At first, a finite element model (FEM-P) is developed assuming perfect bond between concrete, FRP and adhesive interfaces. Then the FEM-P model is expanded to form the FEM-B model by including the bond-slip effect between concrete, FRP and adhesive interfaces. The developed new finite element models (FEM-B and FEM-P) are validated against experimental results and demonstrate to be effective for the structural analysis of FRP strengthened RC beams. Furthermore, parametric studies are carried out to learn the effects of types and thickness of FRP on the structural behavior of FRP strengthened RC beams based on the FEM-B model. The research findings are summarized finally.

Effect of temperature induced bond degradation on fire response of reinforced concrete beams

The influence of temperature induced bond degradation on response of reinforced concrete (RC) beams exposed to fire is presented. A finite element based numerical model is developed in ABAQUS for tracing the response of reinforced concrete beams exposed to fire. Temperature induced interfacial bond degradation between concrete and reinforcing steel is specifically taken into account using bond-link element approach. The effect of temperature dependent local bond stress-slip relations on fire resistance of both normal strength and high strength reinforced concrete beams is investigated. A comparison of numerical model predictions with response parameters measured in fire tests clearly indicate that interfacial bond between reinforcing steel and concrete can influence extent of strength degradation and deflections in RC beams exposed to fire leading to relatively lower fire resistance in the beams. Hence, the current approach of assuming a perfect bond between rebar and concrete in fire resistance analysis of reinforced concrete structures may be un-conservative in certain scenarios, especially for RC beams reinforced with smooth rebars and when rebar temperature exceeds 400°C.