Damage models, particularly the Gurson-Tvergaard-Needleman (GTN) model, are widely used in numerical simulation of material deformations. Each damage model has some constants which must be identified for each material. The direct identification methods are costly and time consuming. In the current work, a combination of experimental, numerical simulation and optimization were used to determine the constants. Quasi-static and dynamic tests were carried out on notched specimens. The experimental profiles of the specimens were used to determine the constants. The constants of GTN damage model were identified through the proposed method and using the results of quasi-static tests. Numerical simulation of the dynamic test was performed utilizing the constants obtained from quasi-static experiments. The results showed a high precision in predicting the specimen's profile in the dynamic testing. The sensitivity analysis was performed on the constants of GTN model to validate the proposed method. Finally, the experiments were simulated using the Johnson-Cook (J-C) damage model and the results were compared to those obtained from GTN damage model.
The present numerical research studies the effect of nano-materials in a lid-driven cylindrical cavity with rotation of circumferential top wall. The heat is transferred from two lateral walls to the domain by constant temperature conditions while other walls are kept isolated. The non-dimensional equations are solved by Finite Volume Method (FVM) and SIMPLEC method. The effect of Reynolds (Re = 100, 400, 1000), Ryleigh (Ra = 104, 105, 106) numbers are studied. In addition, the effect of concentration of nano materials (ϕ = 0%, 1%, 5%), the Height Ratio (HR = 1, 0.5, 2) on Nusselt number, isotherm lines and streamlines are studied. The results show that Reynolds number also can change the effect of nano particles on the heat transfer rate. It is observed that the height ratio increase can improve the Nusselt number since the number and the size of vortices inside the cavity changes. In addition, increase of Ra number can change the flow structure inside the cavity which can help in increasing of Nusselt number.
Purpose The purpose of this paper is to analyze the fatigue life of the crankshaft in an engine with increased horsepower. Design/methodology/approach The applied load on the powertrain components was calculated through a dynamic analysis. Then, to estimate the induced stress in every crank angle, the calculated loads in different engine speeds were applied on the crankshaft. Finally, the critical plane fatigue theories in addition to URM standard were used to estimate the damage and fatigue life of the crankshaft with the increased power. Findings It was found that a simultaneous increase of gas pressure and engine speed by 30 percent will cause an increase of maximum applied load on the crankshaft by 25 percent. It was also found that while the results of finite element (FE) method predict an infinite life for the crankshaft after increasing the power, the URM method predicts an engine failure for the increased power application. In this study, the crankpin fillet is introduced as the most critical area of the crankshaft. Originality/value Increasing the power of the internal combustion engines without changing its main components has been of high interest; however, the failure associated with the increased load as the result of increased power has been a big challenge for that purpose. Moreover, although URM standard provided an efficient practice to evaluate a crankshaft fatigue life, using FE analysis may provide more reliability.
The blade attachment, both dovetail or fir-tree, transfers the centrifugal load from the blade to the disc, generating high mean and peak stresses in notches as well as on contact surfaces. Hence, the strength of the attachment is one of the main concern of the designers for improving the performance of the engine and several optimization procedure have been put forward to minimize the state of stress in the attachment for a given centrifugal load. The optimization process is generally driven by a parametric model. The selection of the proper parameters and their variation ranges represent one of the main issues for the process to converge in a reasonable amount of time. Simulation methods and optimization algorithms have been improved a lot in the past years. Nevertheless, the computational effort of the finite element analysis involved in the optimization procedure of complex geometries remains a critical task. Moreover, an accurate evaluation of the local contact stresses is highly dependent on the mesh refinement, increasing the computing time of the whole optimization process. Moreover, a multi-objective optimization, in addition to robustness design approach, is the designer tool to improve the attachment performance. The searching domain reduction of the optimization process improves the computational performance reducing the convergence time of the solution. To achieve this goal, a preliminary selection of the design space has been performed by means of an analytical approach. This paper describes a new design criterion based on one dimensional approach. The criterion has been implemented in an in-house tool that takes faster decisions, if compared with a two or a three dimensional model, about the number of possible feasible solutions. During the geometrical optimization phase of the blade fir-tree attachment, in which a parametric model is used, the authors try to handle the geometrical non-feasibility with a combination of Latin Hypercube Sampling (LHS) and an adaptive penalty method. The optimization is done via the genetic algorithm and the computational time of the reduced domain is compared with the original one.
There is evidence of a lack of knowledge in the design of the blade/disk attachment so that the strength of the materials is not fully exploited and the load capability of the attachment is underestimated. The aim of this work is to improve the engineers’ capability in designing the attachment so that higher loads can be carried with the same material. To this end, an optimization method has been applied to the attachment design. A dovetail blade root was chosen as case study and the objective function was the static equivalent stress in the blade and the disc. The dovetail was described by variable parameters under geometrical and physical constraints. Optimization was performed with a Genetic Algorithm (GA). The result of the optimization procedure is the optimal set of parameter values that minimizes the equivalent stress on the critical areas. Moreover, a surrogate function was utilized as a booster to the GA to save computational time. Stress analysis was performed with a commercial Finite Element (FE) software to provide the exact fitness value. An in-house code was developed to manage both the optimization process and the input/output interface with the FE software. The same code provides a decision-making core. This core checks for feasibility of the geometry of the current set of parameters. The expected result is an optimized profile in terms of Von-Misses equivalent stress.
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