Papers by Keyword: Debonding

Abstract: Steel and concrete are poured together with a certain way which can be regarded as a fiber reinforced composite material. For this composite material, the issues of bond and pull-out are very important. The bond property of reinforced concrete at normal temperature is different from the property at elevated temperature. The exposure of reinforced concrete structural elements to high temperatures during an aggressive fire leads to significant losses in its structural capacity due to the reduction in the strength of the concrete, possible plastic deformation of embedded steel and most importantly loss of bond between reinforcing steel and concrete. This paper aims to investigate the influence of high temperature to the bond slip of reinforced concrete. The bond behavior between reinforced concrete and reinforcing steel bars was evaluated under elevated temperatures. Based on the energy principle, the debonding criterion of the steel bars and concrete at a high temperature is derived. It was concluded that the bond slip should be included in order to reflect the unloading of the concrete surrounding the reinforcing steel exposed to fire temperature.

Abstract: The study of debonding is of importance in providing a good understanding of the bonded interfaces of dissimilar materials. The problem of debonding of an arbitrarily shaped rigid inclusion in an infinite plate with a point dislocation of thin plate bending is investigated in this paper. Herein, the point dislocation is defined with respect to the difference of the plate deflection angle. An analytical solution is obtained by using the complex stress function approach and the rational mapping function technique. In the derivation, the fundamental solutions of the stress boundary value problem are taken as the principal parts of the corresponding stress functions, and through analytical continuation, the problem of obtaining the complementary stress function is reduced to a Riemann-Hilbert problem. Without loss of generality, numerical results are calculated for a square rigid inclusion with a debonding. It is noted that the stress components are singular at the dislocation point, and a stress concentration can be found in the vicinity of the inclusion corner.

Abstract: Delamination is one of the most common modes of defects of laminated composite shell roofs. A review of literature that exists on composite shells reveals that the research reports on delaminated shells are very few in numbers. Present paper deals with the static analysis of delaminated composite conoidal shells with simply supported boundary condition and subjected to centrally applied point load. For the present study work a finite element approach using eight noded isoparametric shell element with five degrees of freedom per node is employed. A multipoint constraint algorithm is incorporated, to satisfy compatibility of deformation and equilibrium of forces and moments, which leads to unsymmetrical stiffness matrix. This formulation is validated through solutions of benchmark problems. Lamination and extent of delamination area are varied to compare the performances of delaminated conoidal shells against those with no damage. Based on the present comparison some engineering conclusions are also included in this paper, which will serve as future reference.

Abstract: This paper present a energy-based modelling approches for interfacial debonding between steel and concrete. Steel-concrete composite structural member is considered as a generalized elastic body with both the applied load and the interfacial shear stress acting as boundary stresses, and the debonding is modeled as crack propagation along the interface. The energy relationship is discussed in the process of debonding and an energy-based criterion for steel-concrete composite structure is proposed. Following, the debonding process is analyzed through energy-based criterion. The analysis is first performed for special case with constant shear stress along debonded interface, and then for the general case with shear stress softening in the debonded zone. A direct correspondence between energy-based and strength-based analysis can be established for arbitrary softening behavior along the interface. Specifically, through the proper definition of effective interfacial shear strength, the conventional strength-based approach can be employed to give the same results as the much more complicated energy-based analysis.

Abstract: External bonding of fibre reinforced polymer (FRP) composites has become a common way for strengthening concrete members. The performance of the interface between FRP and concrete is one of the key factors affecting the behaviour of the strengthened structure. For this FRP-concrete structure, there are two types of debonding failures: plate end debonding and intermediate crack (IC) induced debonding. This paper presents an analytical solution for the second type debonding failures in FRP-concrete bonded joint model where the FRP plate is subject to tension at both ends. Both the strengthened beam and strengthening FRP are modeled as two linearly elastic Euler–Bernoulli beams bonded together through a thin adhesive layer. The debonding process of the FRP–concrete interface is discussed in detail, and closed-form solutions of bond slip, interface shear stress, and axial force of FRP in different stages are obtained. Parametric studies are further carried out to investigate the effect of the thickness of adhesive layer on the bond behavior of FRP–concrete interface.

Abstract: Coating is one of important parts in fiber-reinforced composite. Under cyclic loading, the effect of coating on interfacial fatigue is investigated based on double shear-lag model. Stresses of components are obtained. Relationship for analyzing interfacial debonding is established by the Paris Formula. Interfacial fatigue on fiber/coating and coating/matrix is simulated. It can be seen that interfacial debonding on different interfaces meet energy conservation law in general.

Abstract: The performance of perforated metallic plates repaired with laminated composite patches is presented in this study. A square aluminum plate with a central circular cutout is considered as a damaged structural element. Numerical studies using commercial finite element code were conducted to investigate the effects of variation in laminate parameters such as number of plies, fiber orientation, and stacking sequences on free vibration responses of the repaired plates. Particular emphasis is placed on the effect of imperfect bonding (patch debonding). A quantitative measure for the effectiveness of the composite patches parameters is taken to be the relative change in natural frequencies of the deboned patches compare to the patches with perfect bonding. The results presented herein indicated that, vibration response of a repaired perforated metallic plate is affected by the number of plies, stacking sequences of the patch and the quality of bonding between the patch and the base plate.

Abstract: The reinforcement of concrete structures with laminates of carbon fibers CFRP (Carbon Fiber Reinforced Polymer) began in the 1970’s but laminates were not used extensively until the 1990’s.Nowadays it is one of the most promising technologies due to the good mechanical characteristics of the laminates and their easy manipulation. In the near future, laminates will play a fundamental role in the rehabilitation projects of buildings. Laminates bond to the concrete by means of resins of epoxy type. The capability of the reinforcement depends directly on the proper behavior of the interface laminate-concrete. The laminate helps to bear loads while the concrete is able to transfer stresses to the laminate. The safety factor of the reinforcement can be guaranteed if we can predict the behavior at the interface between both materials. In this work a test of pure shear has been developed to better understand the behavior at the interface between the laminate and the concrete.

Abstract: Bonding degradation at interface is one of main damage forms of composites, especially under fatigue loading. Interfacial bonding degradation of FRC under two-stage tension loading is studied, which is base for variable-amplitude cyclic loading existing widely in actual engineering. Based on the shear-lag model and considered the asymmetry of interfacial damage, the mechanical governing equations of fiber and matrix are established and related solutions are obtained firstly. Two kinds of loading models are chosen, one is low-high alternate loading, and the other is low early and high late loading. By the aid of the Paris law and the energy release theory, a relationship between debond rate and cycle number is established. Then the interfacial debonding is simulated under the two-stage tension loading. The rules of the crack growth are analyzed for low-high two-stage loadings. It is found that stress amplitude has great influence on interfacial debonding under two-stage loading. Low stress amplitude in a certain range can postpone interfacial bonding degradation. And interfacial damage extent is greater than that under constant-amplitude fatigue loading. Present study is helpful for analyzing the fatigue damage of engineering materials and structures.

Abstract: Interfacial stress distribution of bonded quarter-planes subjected to a concentrated force was re-investigated based on Bogy’s solution[1]. The characteristic length of the singular interface end, δ, was defined, and found varying in a very large size scale with the index of stress singularity from millimeter to nanometer or even smaller scale. The influences the characteristic length scale on the initial debonding of the interface end is a new question worth to pay attention. Photoelasticity experiment was employed to verify whether the initial debonding is always located at interface end with stress singularity. The test results show that the initial debonding does not start from singular interface end if the index of stress singularity is small enough.