Interfacial Stress Distribution Research Articles

Three-dimensional axisymmetric analytical method for pull-out behaviour of adhesive anchors in concrete

The importance of precise prediction of the pull-out behaviour of adhesive anchors in concrete has been emphasised by several researchers. It is known that the pull-out problem of anchors is a three-dimensional (3D) one in nature. However, most of the current analytical studies are limited to one-dimensional (1D) analysis and only few 3D studies are reported in the literature. This paper develops a 3D analytical method for evaluating the pull-out behaviour of adhesive anchors in concrete. In the method, the debonding failure at the anchor-adhesive interface and the concrete cone failure are considered for two cases of boundary conditions. Based on a tri-linear bond-slip model, two sets of closed-form analytical solutions are derived for evaluating the stress fields and the pull-out load throughout the entire loading process. Finally, seven sets of experimental data collected from the literature are used to verify the validity of the analytical method. It is shown that the presented analytical solution can evaluate the interfacial shear stress distribution, the axial stress distribution in the anchor, and the maximum pull-out load of various adhesive anchor systems with reasonable accuracy. It is also found that, when Poisson’s effect is neglected, the closed-form solutions can be reduced to the previous 1D solutions. Although this study is conducted within the context of adhesive anchors, the analytical method is applicable to similar anchorage systems such as bar-to-concrete or fibre-to-matrix bonded anchorages.

Biomechanical finite element analysis of a single implant threaded in anterior and posterior regions of maxilla bone.

The ability of implant dentistry to be a successful alternative for edentulous patients has increased in the last decade. Clinical features such as osseointegration and stability, in addition to the endurance of the integration urged the researchers towards a better understanding of the design parameters that control long term success of the implants. It is therefore necessary to quantify the effect of changing implant design parameters on interface stress distribution within the maxilla bone. A 3D-finite element study was conducted to investigate the effect of changing implant shape parameters (implant body design and implant thread depth) on stress distribution while insertion of the implant in two different regions of maxilla bone (anterior (type III bone) and posterior (type IV bone)). A 3D-CAD geometry of implant-maxilla bone was created through importing digitally visualized CT skull images of a human adult, and then converted into a workable solid body through using a collection of engineering software. Tapered and cylindrical implant models with three different implant V-shaped thread depths (0.25 mm, 0.35 mm, 0.45 mm) were threaded into maxilla bone to investigate the design parameters effect on the final stress status. The proposed implant was of commercial dimensions of 10 mm length and 4 mm in diameter. A vertical static load of 250N was directly applied to the center of the suprastructure of the implant for each model. Evaluations were performed for stress distribution patterns and maximum equivalent Von Mises (EQV) stresses for implants in two regions of maxilla bone under 250N vertical static loading. The obtained results throughout this work showed that, for all models, the highest stresses were located at the crestal cortical bone around the implant neck. The von-Mises stress distribution patterns at different models were similar and higher peak von-Mises stresses of cortical bone were seen in tapered implant body compared to cylinder body in all models. Within the restrictions of the current model, the results obtained can be applied clinically to select properly both implant thread depth and body shape design for a foreseeable success of implant therapy.

Theoretical studies on bidirectional interfacial shear stress transfer of graphene/flexible substrate composite structure

Interfacial mechanical properties have a great influence on the overall mechanical performance of graphene/flexible substrate composite structure. Therefore, it is necessary to study interfacial shear stress transfer between graphene and flexible substrate. In this paper, a two-dimensional nonlinear shear-lag model (2D model) is presented. Taking the effects of Poisson’s ratio of the graphene and substrate into consideration, the bidirectional interfacial shear stress transfer between graphene and flexible substrate subjected to uniaxial tension is investigated by the 2D model when the Poisson’s ratio of substrate is larger than that of graphene. In the elastic bonding stage, the semi-analytical solutions of the bidirectional normal strains of the graphene and bidirectional interfacial shear stresses are derived, respectively, and their distributions at different positions are illustrated. The critical strain for interfacial sliding is derived by the 2D model, and the results show that the critical strain has a micron-scaled characteristic width. The width size of graphene has a significant influence on the critical strain when it is less than the characteristic width, but the size effect can be ignored when the width of graphene is larger than the characteristic width. In addition, the Poisson’s ratio of substrate can also affect the critical strain. Based on the 2D model, the finite element simulations are made to investigate the distribution of graphene's normal strains and interfacial shear stresses in the interfacial sliding stage. Furthermore, compared with the results obtained via one-dimensional nonlinear shear-lag model (1D model), the distributions of graphene’s normal strains and interfacial shear stresses calculated by 2D model show obvious bidimensional effects both in the elastic bonding stage and in the interfacial sliding stage when the width of graphene is large. There exists a compression strain in the graphene and a transverse (perpendicular to the tensile direction) shear stress in the interface, which are neglected in the 1D model. And the distributions of graphene’s tensile strain and longitudinal (along the tensile direction) interfacial shear stress are not uniform along the width, which are also significantly different from the results of 1D model. Moreover, the critical strain for interfacial sliding derived by the 2D model is lower than that obtained by the 1D model. However, when the width of graphene is small enough, the 2D model can be approximately replaced by the 1D model. Finally, by fitting the Raman experimental results, the reliability of the 2D model is verified, and the interfacial stiffness (100 TPa/m) and shear strength (0.295 MPa) between graphene and polyethylene terephthalate (PET) substrate are calculated.

Augmenting the in-situ rock bolt pull test with distributed optical fiber strain sensing

A high spatial resolution distributed optical fiber strain sensing technology is demonstrated to advance the assessment of support element behaviour during in-situ pull tests. A technique to instrument typical tendon support elements with a fiber optic sensor is discussed and was trialed at an underground salt mine through a series of pull tests on instrumented rebar elements. It is shown that a continuous strain profile can be measured along the length of a support element under pull test load, which, in turn, allows the interfacial shear stress distribution and deformation of the support element to be resolved. In comparison to load and displacement measurements solely at the support element head, which is what is traditionally reported for in-situ pull tests, the optical fiber strain sensor is found to provide significantly more insight into the mechanistic behaviour of the support element by readily measuring highly variable strain distributions and by quantifying the load development length of the support element. The sensor arrangement allowed the conventional handling and installation procedures to be followed without any implication to the integrity of the sensor. Accordingly, an instrumented reinforcement element can be installed with minimal interruption to on-going mining/construction procedures at the given project.

Application of digital phase shifting moiré method in interface and dislocation location recognition and real strain characterization from HRTEM images.

In high-resolution transmission electron microscopy (HRTEM) images of heterostructures, it is always difficult to accurately determine the interface position and identify dislocations in a large field of view at tens to hundreds of nanometers due to the small lattice differences. However, in the heterostructure, the determination of the interface position is the key to obtain the true mismatch stress/strain field of the interface. Due to the magnifying effect of the digital moiré method on small differences, digital moiré technology was applied to determine Ge/Si heterostructure interfaces and large-area identification interface dislocations in HRTEM lattice diagrams in this study. By optimizing the frequency and angle of the reference lattice, the interface and dislocation position are clearly and intuitively displayed. How to accurately determine the position of the heterostructure interface and the dislocation of the large-area recognition interface from HRTEM images are studied through simulation experiments. The results show that when the frequency of the reference lattice and the specimen lattice are close, and the angle between them is within 10°, the position of the heterostructure interface can be accurately and intuitively determined by the naked eye according to the distortion characteristics of the moiré fringe. When the frequency of the reference lattice is 0.7 to 0.9 times of the specimen lattice, and the rotation angle is within 8°, the visually clear crossover phenomenon of the moiré fringes is used for large-area identification of interface dislocations. Using the phase measurement interface position sensitivity can reach the Å level. Using the phase-shifting digital moiré method the strain field on the dislocation core at the Ge/Si heterostructure interface and the interface stress distribution were quantitatively analyzed. Compared with the Peierls-Nabarro dislocation model and the Foreman dislocation model, Foreman's variable factor α = 4 is more suitable for describing the strain field of misfit dislocations on the Ge/Si heterostructure interface.

Preparation and SERS properties of petaloid Ag nanostructures induced by regular spontaneous stress distribution

Regular patterned nanostructures are of great importance in functional micro-nano electronic devices and sensing detection. Here, a simple strategy was promoted for fabricating petaloid Ag nanostructures based on Flexible substrate/Metal film (FM) system. The results show that when the interface stress is unsteady, the hexagonal porous on PDMS surface will form regular curvilinear boundary condition to generate uniform interfacial compression stress distribution on the interface of FM system, thus inducing orderly two-dimensional patterns. In this paper, the prepared petaloid Ag nanostructures with small Ag nanoparticles on each petal exhibited sensitive and reliable SERS performance. This simple and feasible method may be beneficial for studying the effect of curve boundary conditions on designing abundant ordered patterns.

Raman imaging of residual stress distribution in epoxy resin and metal interface

AbstractA method for the distribution analysis of residual stress in epoxy resins by Raman microspectroscopy was developed. By using the uniaxial tensile method, a negative correlation between the peak shift of the aromatic C─H stretching vibration and external stress was obtained. By optimizing the precision of the Raman shift measurement, a reliable stress image was obtained for a bulk epoxy resin. This method was applied to the evaluation of the residual stress distribution in epoxy resin/aluminum bonded materials. Raman spectra imaging revealed that stress concentration strongly occurred in the interface of the cured epoxy resin with aluminum, and it was found that Raman spectra images of the small residual stress of the resin interface were affected by the curing process and physical properties of the epoxy resin. Therefore, Raman spectra imaging would appear to have significant potential as a technique for the evaluation of local thermal residual stress in the interface of multimaterial structures.

Analysis of Shear Connector of Steel–Concrete Composite Box-Girder Bridge Considering Interfacial Bonding and Friction

Steel–concrete composite bridges consist of steel and concrete parts which are connected by shear connector such as the widely-used headed stud. Through the chemistry bonding, interface friction and mechanical action the two different materials parts are combined as a composite structure system. Because of the structural mechanism, longitudinal and lateral relative slip and normal separation between the concrete deck and steel girder flange will inevitably exist during the loading process. Further, the complex interface mechanical behavior causes difficulties with nonlinear numerical analysis. Multiple broken lines mode cohesive zone model considering bonding and friction is used in this paper to describe the tangent slip and normal crack of the interface. A zero thickness cohesive element was implemented via the user-defined element subroutine UEL in ABAQUS. Using this method, numerical simulation analysis of a two span composite continuous box-girder was carried out. Results showed load–displacement curves of the structure, relative displacement between the steel girder and the concrete slab interface, interface stress distribution, and internal force of shear studs. Discontinuous deformation numerical simulation has been realized, and effectiveness of the proposed method and accuracy of the program were verified. Although shear stress was assumed to be transmitted by shear connector in the design stage, interface bonding and friction resistance can affect the force state of the shear connector. Results of this study can be used for detailed analysis and evaluation of the composite box-girder bridge without the need to rely on the constitutive laws of shear connectors obtained from push-out tests.

Influence of Inclusions’ Position on Stress Distribution of Inclusion-matrix Interface

In this paper, the influence of inclusions’ position on stress & strain distribution was researched when inclusions were same size and shape. The finite element method was used to study the position effect of inclusions in the FGH95 P/M superalloys. The shape of inclusions was simplified rotundity in the model. The influence of inclusions which was on the surface, in the sub-surface and in the basic material on stress & strain distribution was studied. There were two cases, the inclusion connected basic material tightly and there was a hole between the inclusion and the basic material. The change rule of interfacial stress & strain distribution caused by the variation of inclusions’ position was given.

Effect of interfacial residual thermal stress on the fracture behavior of Cf/B4C composites prepared by spark plasma sintering

Carbon fiber reinforced boron carbide (Cf/B4C) composites were fabricated with different Cfs contents by spark plasma sintering (SPS). The interfacial residual thermal stress (RTS) distribution in the Cf/B4C composites and its effects on the fracture behavior of the composites was investigated based on Raman spectroscopy and finite-element (FE) calculation. The results show that the maximum RTS of Cf in as-produced composites were obtained at the edge of fibers. The B4C matrix among fibers suffered a high compressive and tensile RTS simultaneously in radial and tangential directions, which caused the formation of micro-cracks and became the origin of fracture failure of the Cf/B4C composites. The maximum relative density 98.7% and bending strength of 391.41 MPa were obtained when the Cf content was 2.5% while the maximum fracture toughness of 5.46 MPa·m1/2 at 5% Cf content of Cf/B4C sample. The sharp decreases of bending strength when increasing content of Cf cloth was mainly caused by high RTS in the composites.

A novel approach for the interfacial stress analysis of composite adhesively bonded joints

This paper presents a novel approach for the interfacial stress analysis of composite single-lap joints (SLJ). The analytical modeling is based on the interface elasticity where both the shear and peel stresses are assumed to be variant across the adhesive layer thickness. The unknown interfacial parameters are determined by using an experiment-based inverse method. The finite element simulation is then performed to calculate the interfacial stress distributions and evaluate the effect of the structural parameters on the interfacial behavior of the composite bonded joints. It is shown that both the peel and shear stresses at the interface are influenced by the interface energy and geometry parameters of the composite bonded joint. Numerical results are presented both to demonstrate the advantages of the present model over existing ones and to illustrate the main characteristics of interfacial stress distributions.

Investigation on the interaction mechanism and failure behavior between bolt and rock-like mass

The matching relationship between bolt diameter and borehole diameter determines the bolt supporting effect in the mining roadway. In this paper, the failure modes of the anchorage body under different diameter matching were studied by the pullout test. When the anchorage agent was pulled out completely with bolt, the anchoring effect was ideal. Whereas, when the bolt was pulled out smoothly with only a thin layer of anchorage agent, the anchoring effect was relatively worse. Through multiple pullout tests, the suitable diameter matching difference can be defined with a range of 6–11 mm. Based on the interface sliding failure mode between anchorage agent and rock-like mass, a mechanical model of diameter matching was established. Both equations of tensile force and interfacial shear stress along with the anchorage direction in perfectly elastic state were derived. FLAC 3D was applied to analyze the distribution of interfacial shear stress and axial stress under different diameter matching between the bolt and the borehole. As a result, a 4–11 mm diameter difference shows the best anchoring effect. According to both experimental and simulation results, the optimal diameter matching difference is 6–11 mm.

Interfacial stresses in reinforced concrete cantilever members strengthened with fibre-reinforced polymer laminates

Fibre-reinforced polymers have been increasingly used to strengthen reinforced concrete structures. However, premature brittle debonding failures may occur at the ends of externally bonded fibre-reinforced polymer laminates due to interfacial stress concentrations caused by stiffness imbalances. Although many studies exist on fibre-reinforced polymer-strengthened simply supported beams and slabs, the interfacial stress distributions in fibre-reinforced polymer-strengthened cantilever members are very different from those in simply supported members. Based on the assumptions of linear elasticity, deformation compatibility and static equilibrium conditions, the interfacial stresses in fibre-reinforced polymer-strengthened reinforced concrete cantilever members under arbitrary linear distributed loads were analysed. In particular, closed-form solutions were obtained to calculate the interfacial stresses under either a uniformly distributed load or a single concentrated load located at the overhanging end of the cantilever member. Existing test results on cantilever slabs strengthened by carbon fibre–reinforced polymer sheets were used to verify the model. According to the parametric analysis, the maximum interfacial stresses can be reduced by decreasing the fibre-reinforced polymer thickness, increasing the fibre-reinforced polymer bonding length and increasing the adhesive layer thickness, and by using less rigid fibre-reinforced polymer laminates with high tensile strengths. These results are useful for engineers seeking to optimize strengthening design parameters and implement reliable debonding prevention measures.

Interlaminar damage numerical modelling based on delamination growth of multi-layered composites

A growing interest is nowadays directed towards the numerical modelling and monitoring of the interlaminar damage evolution of composite laminates, but also to the numerical mathematical models and techniques for simulation of the interface delamination. Modelling and investigation of the mechanical behaviour and fracture modes of the multi-layered composites is a complex issue, since other important parameters, such as fibre orientation angles, stacking sequences and configuration of the composite laminates are added to the anisotropic character of the composite materials. Different failure modes may occur on multi-layered composites, while the delamination type fracture may lead to a considerable decrease of the load carrying capacity of the composite structures. Interlaminar stresses, which occur in composite laminates as an effect of the presence of the free edges, have a major influence on the delamination onset and the delamination growth. The paper summarizes the numerical methods and the approaches considered in the simulation of the delamination growth of composite laminates. The obtained results are figured in terms of the opening displacement at the interface crack tip and stress distributions on the plies of the multi-layered composites.

Simulation and measurement of cryogenic-interfacial-properties of T700/modified epoxy for composite cryotanks

Interface between the carbon fiber and epoxy was vital to the mechanical performance of CFRP under cryogenic temperature (−196 °C). In this paper, the cryogenic-interfacial-properties of carbon fiber/modified epoxy (T700/M-Epoxy) under −196 °C were analyzed by experiment, theoretical analysis and finite simulation method (FEM). Experimental data showed that the interfacial shear strength (IFSS) of T700/M-Epoxy at −196 °C was 75.8 MPa, which was increased by 16.1% in comparison with that (65.3 MPa) under room temperature (RT). For theoretical analysis, the microbond sample could be simplified into a cylindrical model. The increase of IFSS at −196 °C derived from contraction deformation of M-Epoxy. FEM was employed to simulate the distribution of interfacial stress and the evolution of debonding in T700/M-Epoxy. Based on the FEM model, both debonding and friction force (148.2 mN, 40.3 mN) at −196 °C were much higher than those (112.6 mN, 21.3 mN) under RT because of coefficient of thermal expansion (CTE) mismatch between T700 and M-Epoxy. The theoretical analysis and FEM simulation made the experimental findings understood well, and they also could be used to predict the interface stress of fiber/resin at cryogenic temperature.

Interfacial stresses of shield tunnel strengthened by a thin plate at inner surface

For tunnel lining strengthened by bonding thin plate at inner surface, premature failure of interface must be avoided to achieve the desired strengthening effect. Therefore, it is significant and urgent to determine the distribution of interfacial stresses between the thin plate and the tunnel lining. In this paper, an analytical solution for predicting the interfacial stresses was developed based on composite beam theory, and its rationality and accuracy were demonstrated through comparisons with the results of finite element analysis and full-scale experiments. On this basis, the interfacial stresses under various parameters were investigated with the verified solution, e.g., buried depth, elastic modulus and thickness of adhesive layer and thin plate. According to the analytical results, the maximum values of interfacial stresses were predicted to occur at the plate end and decrease rapidly with the distance away from the plate end. When steel plate was used as bonded material compared with Carbon Fiber Reinforced Polymer sheet, the interfacial stresses at the plate ends were much larger at the same tensile strength. Higher adhesive layer thickness caused lower interfacial stresses, while higher elastic modulus of adhesive layer and higher thickness and elastic modulus of thin plate led to higher interfacial stresses. The elastic modulus of the adhesive layer was the dominant factor affecting the interfacial stresses. This research is helpful for understanding the interfacial failure mechanism and promoting anti-debonding measures for tunnel lining strengthened by bonding thin plate at inner surface.

Piezoelectric Based Lamb Waves Generation and Propagation in Orthotropic CFRP Plates: II. Influence of Interfacial Stress Distribution

This paper investigates the Lamb wave generation by the surface bonded circular piezoelectric (PZT) actuator and wave propagation within the orthotropic Carbon Fiber Reinforced Plastic (CFRP) plate considering the anisotropy of the elastic and damping properties of the materials; existence of the adhesive layer; and dependence of the interfacial stress distribution on the surface between host plate and actuator, on the anisotropy of the plate material, and on the excited frequency, wavelength and plate thickness. This part of our investigation includes FE based study of the shear stress distribution on the interface between circular PZT actuator and surface of orthotropic CFRP plate, and its dependence on the excited wavelength and plate thickness. The anisotropic elastic and damping properties of the plate material, which are used in the implemented finite element (FE) model, have been preliminary determined in the first part of our investigation. We compare the behavior of the wave generation, propagation and attenuation that are studied using this model with the similar dependencies obtained at the simulation of the non-dissipating plate excited by the periodical radially oriented force, which is distributed along the circumference bounding the actuator, i.e. 3D pin-force excitation case. The proposed results can be used at the design of SHM for the composite structures with the structural anisotropy and damping, and at making a reasonable choice of the frequency, type, dimensions and optimum placement of the actuators and sensors.

Theoretical Predictions of the Interfacial Stress Transfer in Nanotube-Reinforced Polymer Nanocomposites by Using a Strain-Hardening Shear-Lag Model

Interfacial load transfer inside nanofiber-reinforced polymer nanocomposites plays a vital role in capitalizing on the extraordinary mechanical properties of the added nanofibers and in governing their bulk mechanical performance. In this paper, we investigate the load transfer characteristics of nanotube–polymer interfaces by using a micromechanics shear-lag model that takes into account the elastoplastic properties of polymer matrices. Closed-form analytical solutions of the interfacial shear stress distribution profile are derived. The failure of the nanotube–polymer interface and the pull-out force are analyzed using this model based on recently reported nanomechanical single-nanotube pull-out experiments that were conducted on carbon nanotube and boron nitride nanotube polymer interfaces. The theoretical predictions are in good agreement with experimental measurements. The findings from this work are useful to a better understanding of the interfacial load transfer characteristics of nanofiber-reinforced polymer nanocomposites and ultimately contribute to the optimal design and performance of lightweight and high-strength nanocomposite materials. The presented micromechanics model and the analytical solutions can be extended to study the interfacial stress transfer inside 1D nanofiber-reinforced metal and ceramic nanocomposites as well as of 2D material based composites and devices.

Mechanical Behavior of Fiber-to-concrete Interface in Textile Reinforced Concrete: Theoretical Model

This paper presents a theoretical solution of a reinforcement-to-concrete interface model under pull-push loading. Expressions for the interfacial shear stress distribution and load-displacement history are derived for different loading stages. The full debonding propagation process is discussed in detail and the analytical solutions are verified by comparing with existing theoretical models. Results of the analytical solution are presented to illustrate how the bond length and local bond-slip law affect the interfacial bond behavior. While the case study in this paper is on textile reinforced concrete, the analytical solution is equally valid to similar mechanical cases such as rebar reinforced concretes.

Simulation and Analysis on Fiber Reinforced Rubber Matrix Sealing Composite Based on Cohesive Zone Model

A finite element model on the single fiber pull-out test of short fiber reinforced rubber matrix sealing composites (SFRC) were established. The effects of the interphase properties on the interfacial stress distribution and initial debonding strain are investigated based on the cohesive zone model (CZM). The influences of interphase thicknesses and elastic modulus on the interfacial debonding behavior of SFRC are obtained. The results show that the interfacial initial debonding strain increases with the increasement of interphase thickness, and it decreases with the increasement of interphase elastic modulus. An interphase thickness of 0.4 μm and an interphase elastic modulus of about 750 MPa are optimal to restrain the initiation of the interfacial debonding.