Papers by Keyword: Debonding

Abstract: This project is based on the investigation of one characteristic of a new material to improve GFRP high speed vessels constructions. The main objective is to find the debonding, that is the analyzed characteristic that is going to prove that the material works to avoid delamination in the bottom. This characteristic is studied by laboratory reproductions, by designing fiber glass specimens and modifying some of them with viscoelastic, to compare the modified and non-modified ones. The laboratory experiment is based on performing an axial force in the specimen until it separates. By analyzing the force and displacement obtained from the tensile tests, the crack growth rate and stress ratio for each specimen were evaluated. The failure ratio, which allows the evaluation of shear, was also performed.

Abstract: The multi-bolted method is typically used for pultruded GFRP (PGFRP) connections. As the capacity of PGFRP structures is governed by connection strength, many researchers have sought to improve this performance. In a previous study investigating the effectiveness of glass fiber sheets (GFSs) in strengthening multi-bolted connections, debonding failure was observed as a failure mode in various types of GFSs, including 0°/90° and ±45° with 4 and 5 bolts. The present study tested four types of specimens to characterize failure modes when PGFRP is multi-bolted with GFS strengthening. Different failure modes were observed with two different numbers of bolts. Based on the observed failure sequences and previous material properties tested, a calculation equation was proposed. The estimated strength showed good agreement with experimental results. Furthermore, the study highlights some features of the failure load (such as the type of GFS and tensile strength) as recommendations for designing strengthening of PGFRP bolted connections.

Abstract: The use of a carbon fiber composite material to make external prostheses in the form of a femoral socket was the subject of this laboratory study. According to the prior bibliographical studies, this material adapts well to this type of prosthesis. The objective of this research is to study its microscopic structure, in order to verify the good wetting of the fibers by the resin, the good cohesion and molding by infusion. The morphological study of the facies of the parallelepiped-shaped specimens was carried out after cuts perpendicular to the axis of the fiber strands, parallel according to the width and thickness of the specimen. This study was carried out using a scanning electron microscope (SEM), in order to determine, thanks to the typical microstructure of the composite, the various degradations, which appear as a result of the effect of static tension. The laminate used is based on three layers of carbon taffeta fabric and an orthocrylic resin. Tensile tests have been carried out at a speed of 1mm/min with a Zwick/Roell machine with a load cell of 50 kN. This speed was chosen to allow a comparative study with glass fiber specimens, which have been used previously for the production of prostheses, before those made of carbon. The microscopic study allowed to identify the four types of degradation; Matrix fracture, which manifested itself as fault lines, in preferred directions of different sizes. This contributed to interlaminar delamination. The decohesion that contributes to delamination in a different way from that of matrix breakage is visible at different levels. Interlaminar delamination results from the combined effect of matrix breakdown and decohesion and manifests itself as uneven strata. Fiber breakage was manifested by shearing. This study allowed to observing a degradation of the material imposed by static traction. As for the material used in orthopaedics, it has retained good cohesion and meets the requirements of prostheses, despite the defects detected by the microscopic study.

Abstract: Numerical modeling of curved masonry structures reinforced with TRM can be particularly demanding. Indeed, several failure typologies can be encountered when a masonry element is reinforced with this strengthening solution. In the case of arches and vaults, the curvature itself complicates furtherly a correct prediction. The paper wants to provide a reasonable way to model numerically curved masonry structures reinforced with TRM and explore the advantages and detriments of advanced simulation and simplified approaches. At first, an advanced micro-modeling is applied to an arch reinforced at the extrados. Then, the same approach is applied to a limited portion of the same arch and numerical lap shear tests are performed. Finally, a simplified model equipped with a set of truss elements is proposed.

Abstract: The studies contained in the current literature particularly emphasize the importance of the role of the local bond mechanism on the global performance of fiber reinforced polymer systems (FRPs) employed for the strengthening and the rehabilitation of structures. Nevertheless, although several applications of FRPs involve curved masonry structures (arches, vaults, domes, etc.), the bond mechanism of FRPs applied on masonry samples with curved substrates is a topic still scarcely investigated and the actual guidelines do not provide specific design formulas. The aim of the present paper is to analyze the main features characterizing the bond behavior of FRPs externally applied to masonry specimens with a curved substrate configuration throughout a simple modeling approach based on the interface concept. Particular consideration is devoted to the development of suitable constitutive laws for the FRP/masonry interface. Considering case studies derived from the current literature, consisting of shear-lap bond tests of curved masonry specimens characterized by different curvatures of the bonded surface and different strengthening configurations, numerical analyses are carried out in order to emphasize the ability of the model to capture the bond behavior of FRP applied on curved masonry substrates.

Abstract: In this study, the fatigue fracture criterion of the adhesively bonded joint is discussed. The singular stress field is formed at the interface end in the butt joint and causes the debonding fracture. The singular stress field is represented with the intensity of singular stress field (ISSF). The static debonding strength of the adhesively bonded joints is expressed with a constant value of critical ISSF. The rotating-bending fatigue tests are carried out on the butt joints of 15mm in diameter with four different adhesive thicknesses of 109 - 159μm, 209 - 265μm, 393 - 432μm and 754 - 841μm. The evaluation method by the ISSF is applied to the experimental results. It is found that the fatigue strength of the butt joint can be expressed with the constant value of critical ISSF.

Abstract: The present article addresses the evaluation of the electro-mechanical (E/M) impedance method as a Structure Health Monitoring (SHM) method to detect and classify damage, more specific, the debonding of a face layer.In the study the considered structure is simplified as a circular sandwich panel of constant thickness, consisting of isotropic face layers and a honeycomb core.The debonding is assumed to be circular and situated at the center of the panel, only variable in its radius.The article starts with a brief introduction to the basic idea of SHM and the fundamentals of the E/M impedance method.Further, the idealized setting is investigated by two sets of experiments whose results are analyzed by typically used damage metrics and by considering both analytical and numerical models.A coupled-field FEM model is developed and compared to the experimental results.Furthermore, an analytical model is derived to evaluate the experimental and numerical results.All results are presented and discussed extensively on pursuing the objective to detect and classify the size of a debonding.Finally, it is shown how a model based approach can predict the presence but also the size of a debonding in the considered sandwich panels based on the E/M impedance measurements.

Abstract: Shear strengthening of RC beam with adhesively bonded carbon fiber reinforced-polymer (CFRP) laminates is becoming both environmentally and economically more preferable than replacement. However, the early separation of these plated stripes was the most critical failure which leads to prevent reaching the full capacity required from the strengthening. This study aims to present a new method to prevent debonding failure of CFRP laminates adhesively glued to concrete surface using embedded connectors to enhance the interfacial bond strength. Therefore, steel bar and adhesive connectors were fabricated and used at the interface of the bonded CFRP laminates. Five beam specimens including one control beam were tested to investigate the effects of the connectors to prevent or delay the premature debonding of the EB CFRP laminates. The experimental results showed that both steel and adhesive connectors completely prevented premature debonding failure of CFRP shear strip and allowed the beams to fail by flexure with full ductility and strength. Steel and adhesive connectors would enhance 33% and 38% failure loads respectively as compared to strengthened beam without connectors.

Abstract: Concrete patch repair is becoming an important facet of the civil construction industry when considering the large quantity of exposed concrete surfaces requiring maintenance and rehabilitation during its design life cycle. Patch repairs are more often than not done with a specialized polymer-modified mortar which requires adequate quality control and quality assurance during application and curing to ensure long-term success. Unfortunately, there have been many patch repair projects where there has been poor performance of the patch repairs resulting in debonding, cracking and discolouration. In this paper, poor or inadequate quality control during the patch repair process is investigated as one of the possible reasons for poor performance and premature failure . It is postulated that because of the lack of adequate knowledge and understanding of the repair material and the repair process by the various stakeholders (applicator, supplier, consultant and client), deficiencies in the quality control and quality assurance before, during and after the repair project often exists. In many patch repair projects, the responsibility for the successful completion of the patch repair work and the assessment of long term performance of patch repairs is not fully embraced by all of the parties involved.This postulation has led to the research, by using questionnaires designed specifically for the four different stakeholder categories of the concrete repair industry. The results indicate that there is very little discussion amongst the stakeholders regarding quality control and acceptance criteria when performing concrete patch repairs, neither for the identification of patch repair failure directly after the completion of the patch repair, nor for long term performance of the patch repairs.

Abstract: This paper presents the results of experimental and theoretical studies justifying the possibility of using infrared (IR) thermography for detection of deformation debonding of composite material from a reinforced concrete structure that occurs under operating conditions and develops according to the cohesion scenario. The analysis of the results allowed us to determine the optimal inspection parameters of IR thermography to assure best registration of the presence of fiber composite material debonding from the surface of a concrete structure. It has been found that the most accurate and timely information about debonding in a carbon fiber sheet/epoxy/concrete/delamination/concrete system can be obtained during the cooling stage after pulse heating of the structure surface, since at this stage the magnitude of thermal response to debonding reaches its maximum.