23 research outputs found
Impact damage characteristics of carbon fibre metal laminates : experiments and simulation
Get PDFIn this work, the impact response of carbon fibre metal laminates (FMLs) was experimentally and numerically studied with an improved design of the fibre composite lay-up for optimal mechanical properties and damage resistance. Two different stacking sequences (Carall 3–3/2–0.5 and Carall 5–3/2–0.5) were designed and characterised. Damage at relatively low energy impact energies (≤30 J) was investigated using Ultrasonic C-scanning and X–ray Computed Tomography (X-RCT). A 3D finite element model was developed to simulate the impact induced damage in both metal and composite layers using Abaqus/Explicit. Cohesive zone elements were introduced to capture delamination occurring between carbon fibre/epoxy plies and debonding at the interfaces between aluminium and the composite layers. Carall 5–3/2–0.5 was found to absorb more energy elastically, which indicates better resistance to damage. A good agreement is obtained between the numerically predicted results and experimental measurements in terms of force and absorbed energy during impact where the damage modes such as delamination was well simulated when compared to non-destructive techniques (NDT)
Increasing bending angle in thick-walled pipes with wide heating
No full textThe spot heating of a metal part leads to many small deformations. The applications of this method are straightening the bridge parts, turbo-machinery shafts, and so forth. The movement of the heat source on a given path (line heating) leads to an increase in the deformation and the possibility of creating complex bends. However, it is complicated to predict and control the path and velocity of the heat source as well as determining the heat intensity. In the pipes, this method requires simultaneous control over the two torches on both sides of the pipe. The present study aims at investigating the mechanism of deformation and increasing the bending angle in thick pipes by means of a simple heating method. At first, the maximum bending in heating a large circular zone (entitled “wide heating”) is obtained by simulating the process using finite element method and optimizing it applying the genetic aggregation algorithm. Then, a new method for simultaneous heating within two zones is introduced. The interaction between two zones leads to the development of the shortening mechanism in the pipe wall and a significant increase in the bending angle. In this method, there is no need to move the torch where the temperature is controlled more accurately. To evaluate the finite element model, several pipe heating tests are performed with their results being agreed well with the simulation results
FAILURE AND COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF PLATEN SUPERHEATER TUBES IN A 320 MW POWER PLANT TO PROVIDE AN OPTIMAL LAYOUT DESIGN
No full textBoilers are one of the most important parts of the power plants. Superheater
tubes have the main role in boilers and are subject to degradation because of
many working conditions. According to the pressure and temperature of the
working condition of the superheater tubes in boiler, failure is usually reported from the superheater tubes. Therefore, identifying the causes of this failure and its prevention is quite important. The reports on the failure of platen superheaters in several similar boilers whose inlet and outlet header is the same for all tubes indicate that a particular part of the tubes is more vulnerable than the rest in tubes and the failures are concentrated there. Location of the most failures is at the end of the 135-degree bend of the platen superheater. Therefore, this case was investigated at a special 320 MW power plant where there were seven units. The objective of this investigation is to find the cause of the failure and solve the problem for working in a long time with safety. The preliminary examination showed that the damaged point in this group had a higher temperature than the other groups in the same position. To prove the existence of the higher temperature at these points, three methods were used: metallography, oxide layer thickness measurement, and CFD analysis and all the three methods confirm the results. In this paper, different solutions were introduced for the 320 MW power plant issue. Each of the solution methods is subject to certain advantages and disadvantage. Following the analysis, among the solution methods, one of them was selected as the best solution. Based on the method, some schemes were offered as suggested plans as an alternative to the platen superheater tubes. These schemes were validated in comparison to the power plant superheater. Then, the investigation focused on the geometry of schemes. In addition, all of the three schemes were analyzed by CFD method. Based on the analytical results, one of the schemes was chosen as an alternative plan to the platen superheater for the power plant
Bending improvement in Spot Heating of pipes in comparison with Line Heating method
No full textIn Spot Heating, a small area of a metal part surface is heated quickly with a gas torch, laser beam, or induction coil to a temperature below the phase change temperature and then cools down. The heated area undergoes compressive plastic strain and the part gets deformed. This method is usually applied as trial and error for straightening shafts, bridge components, ship structures, etc. The conventional straightening mechanism in industries involves creating thermal gradient mechanism (TGM) and shortening. Many studies have been conducted for bending of thin pipes (at a maximum thickness of 2 mm) with the induction of “shortening” by laser. Spot Heating, despite its simplicity, results in very small deformations. The present study aims to increase the deformation in the Spot Heating method so as to extend its use in pipe straightening. To meet this goal, the shortening mechanism is developed through a thick pipe wall by optimizing the heating parameters. CFD analysis of flame flow is carried out to determine the heat flux distribution over the pipe surface. Also, the finite element method and optimization are used to analyze and raise the pipe deformation mechanism. The results indicate a considerable increase in the pipe bending which reduces the stages necessary for the pipe straightening in industries. Furthermore, the appropriate distance for combining the hot spots is also obtained. To evaluate the results, the Spot Heating test is performed, showing appropriate agreement with the simulation results
Sex‐specific repolarization heterogeneity in mouse left ventricle: Optical mapping combined with mathematical modeling predict the contribution of specific ionic currents
No full textAbstract Ventricular repolarization shows notable sex‐specificity, with female sex being associated with longer QT‐intervals in electrocardiography irrespective of the species studied. From a clinical point of view, women are at a greater risk for drug‐induced torsade de pointes and symptomatic long‐QT syndrome. Here, we present an optical mapping (OM) approach to reveal sex‐specific action potential (AP) heterogeneity in a slice preparation of mouse hearts. Left ventricular epicardial repolarization in female versus male mice shows longer and, interindividually, more variable AP duration (APD), yielding a less prominent transmural APD gradient. By combining OM with mathematical modeling, we suggest a significant role of IKto,f and IKur in AP broadening in females. Other transmembrane currents, including INaL, only marginally affect basal APD. As in many cardiac pathophysiologies, increasing [Ca2+]i poses a risk for arrhythmia, the response of AP morphology to enhanced activation of L‐type calcium channels (LTCC) was assessed in a sex‐selective manner. Both APD and its variation increased significantly more in female versus male mice after pharmacological LTCC activation, which we hypothesize to be due to sex‐specific INaL expression based on mathematical modeling. Altogether, we demonstrate a more delayed repolarization of LV epicardium, a leveled LV transmural APD gradient, and a more pronounced epicardial APD response to Ca2+ influx in females versus males. Mathematical modeling quantifies the relative contributions of selected ionic currents to sex‐specific AP morphology under normal and pathophysiological conditions
Multimaterial laminated composites: An assessment of effect of stacking sequence on flexural response
No full textAn investigation on blunt notch behavior of fiber metal laminates containing notch with different shapes
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Analysis of Fatigue–Creep Crack Growth in the Superheater Header of a Power Plant Boilers and Estimation of Its Remaining Lifetime
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