Papers by Keyword: Debonding

Abstract: Several different methodology for the study of adhesively bonded joints can be found in literature. However, most of those methods are joint-specific. One of the most interesting joint case is the bonding between the skin and the stringer of an aeronautical panel. Unfortunately, this case is one of the less studied, due to the complexity of the load conditions. In this paper, the problem of the skin stringer debonding under a T-pull load condition is analyzed. The analysis is performed by means of the methodology developed by Bigwood and Crocombe, that differs from other bonding technique because it is not joint-specific. Indeed, this method allows to solve any type of joints for which it is possible to specify the end loading values on every adherends’ sides. The results, in terms of peel and shear stress, are compared with the ones obtained via finite element methods, in order to validate the results for the specific load case considered.

Abstract: In this study, effect of thermal cycling after water absorption on flexural property of CFRP(Carbon Fiber Reinforced Plastics) was examined. Water absorption tests were conducted for 24 hours, 100 hours and 500 hours at 90^°C. Thermal cycling test was conducted by using water absorbed specimen. The temperature range of thermal cycling test was from room temperature to-196^°C. The static three-point flexural test of CFRP with freezing after water absorption was conducted based on JIS(Japanese Industrial standard) K 7074. Following conclusions are obtained. In case of immersion for 24 hours, flexural strength and modulus of CFRP with freezing after water absorption decreased with an increase of the number of cycles. In case of immersion for 100 hours and 500 hours, flexural strength and modulus of CFRP with freezing after water absorption did not change. The water absorption of CFRP was the phenomenon that the water penetrated into fiber/resin interface. So, in the case of immersion for 24 hours that the absorption time is not so long, damage progresses gradually in thermal cycling test. On the other hand, in the case of immersion for 500 hours is long, the damage progresses at the early stage of the thermal cycling test, and after that the damage does not almost progress.

Abstract: Mechanism of CNT-metal bonding is investigated using molecular dynamics in this study. Both bonding and debonding process are considered. It is shown that the bonding can be achieved at a temperature lower than the melting point. The surface melting and capillary wetting dominate the bonding process. In addition, there are two potential failure positions, one is at CNT-Ni interface and the other is at nickel surface which are determined by the strength competition of these two interfaces. To obtain high bonding strength we should form coalescence structure between CNT and the metal at a higher temperature to achieve larger contact length. Also we find that the debonding process experiences elastic deformation followed by debonding at CNT-Ni or Ni–Ni interface.

Abstract: There has been much research conducted on the current performance of Fiber Reinforced Polymer (FRP) as reinforcement. It was due to FRP easier to maintain than steel during construction because of less weight. Laboratory works on the flexural behavior of concrete beams that with GFRP and CFRP use as a plate strengthening for the beam size 2800 x 200 x 250 millimeter. study of the pattern of cracking and failure modes of the beam will be compared between the ten types of beams consisting of steel reinforced beams , beam-reinforced GFRP and GFRP reinforced beams strengthened with CFRP with different lengths. Comparing between the beam bending performance was examined through the ultimate load, cracking and failure modes.

Abstract: Functionally graded materials (FGMs) have become helpful in our engineering applications. Analysis of functionally graded material (FGM) plate during debonding case with different boundary conditions is the main purpose of this investigation. Elastic modulus (E) of functionally graded (FG) plate is assumed to vary continuously throughout the height of the plate, according the volume fraction of the constituent materials based on a modified sigmoid function, but the value of Poisson coefficient is constant. In this research, the finite element method (FEM) is used in order to show the shape of a plate made of FGM during debonding case with different boundary conditions. In the present investigation, the displacement value applied to the FGM plate is changed in order to find the relationship between the maximum von Mises stress and the displacement. Also, the relationship between the maximum shear stress and the displacement is carried out in the present work. The material gradient indexes of the FGM plate are changed from 1 to 10. The stress distributions around the debonding zone with all the material gradient indexes of the FGM plate are investigated in this work.

Abstract: Experimental and numerical results show that the predominant failure mode of FRP strengthened masonry structures is the interfacial debonding, which occurs prior to reaching the compressive strength of the substrate and/or the tensile strength of the FRP composite. In this paper, a three-dimensional numerical model is developed to simulate the experimental response of direct shear test of FRP-masonry joints and. A damage model is adopted for both mortar and bricks characterized by a different behavior in tension and compression.

Abstract: This paper sheds light into the effect of the periodic pattern of bricks and mortar joints on the load-carrying capacity of the interface between fiber-reinforced polymer (FRP) composites and masonry. Two simplified cohesive material laws are proposed for the FRP-mortar and FRP-brick interfaces, which allow for the computation in closed form of a finite effective bond length L_eff of the interfaces. The aforementioned simplified interfacial laws are employed to compute the load response of the FRP-masonry interface, and to obtain the interfacial shear stress, the FRP axial strain, and the slip profiles along the bonded length. The results indicate that length of the stress-transfer zone (L_STZ) of the FRP-masonry interface varies periodically as its location shifts with respect to the position of the mortar joints. Furthermore L_STZ can be different from the effective length of the FRP-brick interface and is influenced by the size of the bricks and mortar joints.

Abstract: For the shear strengthening of masonry walls, different configurations for FRP sheets are currently used in real application, such as vertical, horizontal or diagonal strips. In the last configuration the FRP sheet is inclined with respect to the direction of mortar joints. In the experimental campaign presented in this paper, it is investigated whether the FRP-masonry bond could be affected by this inclination. In order to analyze this issue, three different typologies of masonry panels (with different textures) retrofitted by FRP sheets, inclined of 45 degrees with respect to the vertical axis of the specimen, are subjected to single-lap shear tests. Results of shear tests are presented in terms of maximum debonding forces, force-elongation curves, failure modes and strain profiles along the specimens. The use of Digital Image Correlation (DIC) technique allowed to obtain complete strain maps on the surface of the specimens tested, with the purpose of investigating possible variations in the strain field within the bonded area.

Abstract: The first results of an experimental campaign are reported that evaluates the efficiency of anchored CFRP reinforcements on brick masonry. Near End Supported Single Shear Tests were carried out on masonry pillars made according two different patterns, in order to detect the influence of both bed and perpend joints. The results are compared with results obtained from previous experimental campaign in which CFRP reinforcements were applied on “only brick” surfaces.

Abstract: This paper studies the effect of lamination and fiber orientation on the geometrically nonlinear dynamic response of debonded regions in walls strengthened with FRP. The paper adopts an analytical/numerical approach and uses a specially tailored finite element formulation for the layered structure. By means of this analytical/numerical tool, two strengthening layouts for a wall segment subjected to a dynamic shear loading are compared. In the first layout, the fibers are oriented along the width and height of the segment and in the second one, they are oriented along its diagonals. The analysis reveals that the two layouts are involved with significantly different critical points and significantly different dynamic post-buckling behaviors. Specifically, it shows that the diagonal layout, which better serves the shear loading scenario, is involved with a much smaller critical displacement and a dynamic post-buckling behavior that is governed by the stiffer compressed and tensed diagonals.