Papers by Keyword: Composite Repair

Abstract: Pipeline system is one of the essential infrastructures in oil and gas industries as it is used to transport oil and gas over long distance. However, pipelines will undergo damages and deteriorations after being used for some years, especially when corrosion occurs. Corrosive pipes will experience reduction in wall thickness resulted a lower remaining strength of the pipe, and consequently lead to failure once the remaining strength unable to withstand the desired operating pressure of the pipe. Therefore, additional strength from repairing job needs to be provided, for instance, by using fibre-reinforced polymer (FRP) composites. Unlike the corroded pipeline assessment codes, the pipeline repair codes that are used to design composite repair system of corroded pipe do not include the defect geometries such as defect length. In this study, burst pressure of the composite repaired pipeline with different defect lengths and the effect of the defect length upon the burst capacity of composite repaired pipe are investigated. The study is carried out by finite element analysis on various defective pipes with different defect length sizes. The results show that the difference of the burst pressure subjected to various defect lengths is 15.59% and this had proved that there is effect of defect length upon the burst capacity of composite repaired pipe. This finding can be very useful for optimizing the existing repair design.

Abstract: This paper focuses on the cracks repair of A5083 aluminum alloy widely used in marine structures. Indeed, these latter are under continuous high loadings which, with time, cause fatigue of the material and finally damage and crack propagation. Composite patches play an important role in repairing damaged structures by cracking in order to restore them as much as possible to their original operating state. In this study, we compare performance and efficiency between two patches made in carbon-epoxy and boron-epoxy with four different shapes: circular, rectangular, trapezoidal and elliptic. The loading and crack lengths effects on the performance of these patches were also studied. This numerical investigation was carried out to highlight the evolution of the J-integral as a function of the applied load, the geometrical shape of the patch and the crack length for both types of composites. According to the obtained results the best performance for the improvement of crack propagation resistance in aluminum alloy marine structures was achieved by using a circular patch in boron-epoxy.

Abstract: This paper evaluates the feasibility and effectiveness, within controlled conditions of an active pitch catch sensing PZT sensors on two panels and an aircraft structure made from carbon fiber reinforced plastic (CFRP) pre-impregnated materials. Once cured, the exhibits were subjected to partial and full penetration damages. Two PZT sensors each acting as an actuator and receiver were placed across the investigated region at 100mm apart. Three conditions were set on each panel for each undamaged, damaged and repaired area. Fifty readings were carried out on each panel for each condition. Feature extraction of the wavelet propagations were applied for the post processing from the captured Lamb wave data. The aircraft structure was also used to acquire data with the same above condition. A promising result shows that the interrogation of the actuating PZT sensors can differentiate the studied condition for both panels and structure. In addition, distinguished wavelet patterns were contributed by the surface irregularities due to damage and additional repair plies for both panels and aircraft structure.

Abstract: In this study, the three-dimensional and nonlinear finite element method is used to estimate the performances of bonded composite repairs of metallic cracked aircraft structures by analyzing the J integral and at the crack tips of repaired cracks for single and double symmetric patches. Several calculations have been realized to extract the plasticized elements around the crack tip. The obtained results show that composite repair reduces significantly the J integral at the crack tip which can improve the fatigue life of aircraft structures. It was also shown that the double symmetric patch has a considerable beneficial effect on the repair performance compared to the single patch.

Abstract: More and more advanced composite materials are used in mainly supporting structure of civil aviation; its airworthiness safety should be the focus of the research. Damage assessment is the key step in the general composite repair procedure. In this paper, the ANSYS calculating method is validated on the basis of classic laminate theory which could be used to calculate composite strength. In one case, it is applied to simulation and modeling of the B767 landing gear door. The case shows that composite damage mode such as low velocity impact damage, curing and fatigue could be evaluated with finite element method, the result of evaluation is provided as a means to composite damage assessment. Thereafter, the finite element method can be used for structural health monitoring to advanced composites.

Abstract: Abstract. Internal and/or external corrosions may frequently occur in pressurized pipes in offshore engineering components and many other industries. Corrosion defects reduce the collapse load of pipes, which can be improved by composite repairs. In this article, elastic-plastic finite elements analyses of pressurized repaired pipes with internal longitudinal flaws are performed to obtain the plastic collapse loads of them. The effects of composite patch geometries such as thickness and length on the improved collapse loads of repaired pipes are investigated. It is shown that the limit load of the repaired pipes may reach to the un-defected pipe by increasing the patch thickness (i.e. 25% of flaw depth for the pipe and patch material used in this study).

Abstract: At present, aircraft structural integrity is a concerned due to heavy usage of composite materials and cost saving on the operational. Structural health monitoring system is one of condition based monitoring introduced to supplement the current aircraft maintenance non destructive inspection. One approach is to embed or attach sensors such as lead zirconate titanate (PZT) to detect the anomalies either passively or actively. Due to the aircraft operational environment the defects and damage are likely to occur. Repair has to be carried out as per recommended and the requirement to replace back the sensors are important in order to monitor back the structure at post repair situation. The Lamb waves generated by using the PZT sensor can be used to monitor the surface structural integrity for damage or pristine condition. The effect of the lamb wave signals when surface condition of the aircraft component changes is concerned. One hundred data sets were recorded for the undamaged, damage and repair condition. An outlier analysis was used to analyze the situation by overlaying the isolated signal spectrum and the range of the voltage peak to peak (Vpp) mean values. Different signals were observed for different type of structural condition tested and more tests were required to make a conclusive solution.

Abstract: This paper provides a new method to repair the steel pipe with fatigue cracks by using carbon fiber reinforced polymer (CFRP). Cracks may arise in Pressure pipeline in service because of low cycle fatigue. Crack defect is the biggest problem, because crack will gradually propagate and seriously threaten the safe operation of pipeline. This paper provides a repair and calculation method for pressure pipeline with fatigue cracks, and some specific engineering cases are given based on this method.

Abstract: This work reports on the experimental and numerical study of the bending behaviour of two-dimensional adhesively-bonded scarf repairs of carbon-epoxy laminates, bonded with the ductile adhesive Araldite 2015®. Scarf angles varying from 2 to 45º were tested. The experimental work performed was used to validate a numerical Finite Element analysis using ABAQUS® and a methodology developed by the authors to predict the strength of bonded assemblies. This methodology consists on replacing the adhesive layer by cohesive elements, including mixed-mode criteria to deal with the mixed-mode behaviour usually observed in structures. Trapezoidal laws in pure modes I and II were used to account for the ductility of the adhesive used. The cohesive laws in pure modes I and II were determined with Double Cantilever Beam and End-Notched Flexure tests, respectively, using an inverse method. Since in the experiments interlaminar and transverse intralaminar failures of the carbon-epoxy components also occurred in some regions, cohesive laws to simulate these failure modes were also obtained experimentally with a similar procedure. A good correlation with the experiments was found on the elastic stiffness, maximum load and failure mode of the repairs, showing that this methodology simulates accurately the mechanical behaviour of bonded assemblies.