Department of Mechanical Engineering
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Item Simulation of Delamination Crack Growth in Composite Laminates: Application of Local and Non-Local Interface Damage Models(University Research Journal of Engineering & Technology, 2015-03-17) Muhammad Asad; [at- al.]The use of composite laminates is increasing in these days due to higher strength and low density values in comparison of metals. Delamination is a major source of failure in composite laminates. Damage mechanics based theories are employed to simulate the delamination phenomena between composite laminates. These damage models are inherently local and can cause the concentration of stresses around the crack tip. In the present study integral type non-local damage formulation is proposed to avoid the localization problem associated to damage formulation. A comprehensive study is carried out for the selection of different non-local variables. Finite Element simulations based on proposed non-local damage models and classical local damage model are performed and results are compared with available experimental data for UD IMS/924 Carbon/fiber epoxy composite laminate.Item Optimization of lamp arrangement in a closed-conduit UV reactor based on a genetic algorithm.(Water Science & Technology, IWA, 2016-03-02) Ahmad, ZeshanThe choice for the arrangement of the UV lamps in a closed-conduit ultraviolet (CCUV) reactor significantly affects the performance. However, a systematic methodology for the optimal lamp arrangement within the chamber of the CCUV reactor is not well established in the literature. In this research work, we propose a viable systematic methodology for the lamp arrangement based on a genetic algorithm (GA). In addition, we analyze the impacts of the diameter, angle, and symmetry of the lamp arrangement on the reduction equivalent dose (RED). The results are compared based on the simulated RED values and evaluated using the computational fluid dynamics simulations software ANSYS FLUENT. The fluence rate was calculated using commercial software UVCalc3D, and the GA-based lamp arrangement optimization was achieved using MATLAB. The simulation results provide detailed information about the GA-based methodology for the lamp arrangement, the pathogen transport, and the simulated RED values. A significant increase in the RED values was achieved by using the GA-based lamp arrangement methodology. This increase in RED value was highest for the asymmetric lamp arrangement within the chamber of the CCUV reactor. These results demonstrate that the proposed GA-based methodology for symmetric and asymmetric lamp arrangement provides a viable technical solution to the design and optimization of the CCUV reacto.Item A parametric sensitivity study on preforming simulations of woven composites using a hypoelastic computational model(Journal of Reinforced Plastics and Composites, SAGE, 2016-02-01) Asad, MuhammadPreforming simulation for structural composite processing can significantly assist in the development of forming tools, prediction of manufacturing issues, optimization of process parameters and structural design analysis. The present study is aimed at investigating the influence of some important parameters in composite forming using a hypoelastic computational model developed for simulating the deformation behaviour of fibrous materials. The process parameters considered within this numerical work investigate the effects of binder force, coefficient of friction and forming speed. The study is conducted using two most commonly used double-curvature geometries for analysis of woven composites: double dome and hemisphere. It has been shown with this comprehensive study that the forming simulations are greatly affected by the choice of process parameters, and models based on finite element approach, such as the proposed hypoelastic model, can only predict its effects.Item Some insight on the modeling of chip information and its morphology during metal cutting operations.(Comptes Rendus Mecanique, Elsevier, 2015-08-22) Asad, MuhammadThe present paper deals with the mechanisms of chip formation during cutting operations. It deals with some experiments characterising the chip morphologies and microstructure chip investigations under high loadings. In this contribution, mechanisms of chip segmentation are presented. The effect of cutting conditions on cutting forces is treated. Consequently, the chip segmentation phenomenon was correlated to cutting forces evolutions. Also, an investigation on chip strain localisation is carried out. Numerical simulations dealing with chip formation and considering thermomechanical phenomena are also presented. Some numerical results related to chip formation based on the theory of strain gradient plasticity are also discussed. Moreover, the effect of machining system stiffness on chip segmentation is analysed.Item A numerical approach on parametric sensitivity analysis for an aeronautic aluminium alloy turning process(Mechanica, 2016-03-15) Asad, MuhammadThe understanding of physical parameters of machining processes of aerospace grade aluminium alloy is always of prime importance. The main concern is always to understand the chip formation process and the resultant cutting force experienced by the tool due to different parameters like cutting speeds, feed rate, friction coefficient and tool rake angle etc. The finite element analysis has replaced many expensive and time consuming physical machining processes. In the present work, an extensive study of different parameters affecting the turning process of aluminium alloy (A2024-T351) is performed using finite element analysis. The Johnson-Cook ductile material model based on coupled plasticity and damage evolution is employed to simulate the cutting process. The authenticity of the performed simulation work is verified by comparing the simulation results with available experimental data on machining of aluminium alloy (A2024-T351).Item A parametric sensitivity study on preforming simulations of woven composites using a hypoelastic computational model(Journal of Reinforced Plastics and Composites, 2015) Muhammad A Khan; Waqas Saleem; Muhammad Asad; Hassan IjazPreforming simulation for structural composite processing can significantly assist in the development of forming tools, prediction of manufacturing issues, optimization of process parameters and structural design analysis. The present study is aimed at investigating the influence of some important parameters in composite forming using a hypoelastic computational model developed for simulating the deformation behaviour of fibrous materials. The process parameters considered within this numerical work investigate the effects of binder force, coefficient of friction and forming speed. The study is conducted using two most commonly used double-curvature geometries for analysis of woven composites: double dome and hemisphere. It has been shown with this comprehensive study that the forming simulations are greatly affected by the choice of process parameters, and models based on finite element approach, such as the proposed hypoelastic model, can only predict its effects.Item A Numerical Approach on the Design of a Sustainable Turning Insert(2014) Muhammad Asad; Adnan Ahmed Naeem; Syed Rehan Ashraf; Tayyab RabbaniTo decrease the energy footprint of a machined product, a novel turning insert design has been reported in this work. Two geometrical models of the turning inserts: a commercially available design of insert and proposed design of insert have been used to numerically simulate the turning operation. FEM based coupled temperature displacement simulations for orthogonal turning operations for A2024-T351 are carried out. Reasonable associations of numerical results with the experimentally published result were found. Numerical simulation results show the efficacy of the new design of the insert in quantitative reduction of energy inefficient by product of machining named as ―Burr‖. Additionally an improved tool life has also been predicted.Item Short Circuit Stress Calculation in Power Transformer Using Finite Element Method on High Voltage Winding Displaced Vertically(2013) Ashfaq Ahmad; Iqra Javed; Waseem NazarThe objective of this research is to compute the mechanical stresses in power transformer resulting from the currents more than rated value during its operation. Due to this high fault current, mechanical stresses are produced indifferent directions which may cause the damage of winding insulation. Various techniques have been adopted to analyze the stresses on transformer windings. For the accomplishment of research, FEM (Finite Element Method) is utilized for the calculation of short circuit forces. All mechanical generated in transformers are calculated mathematically and verified through software. For the verification of results, real time measurements on 20MVA 132 /11.5KV power transformer are made. Various failure mechanisms due to these forces have been discussed. Moreover, design parameters which determine the maximum stresses in different parts of the transformer are also the part of research. Effects of asymmetrical current and forces in various parts of transformer have also been narrated. Moreover, Different properties of materials have been studied and the usage of proper material for withstanding the dynamic effects of short circuits is discussed. Workmanship errors on short circuit withstand capability have also been elucidated. Finally, a complete model for the study of dynamic effects of short-circuits in a power transformer and comparison with forces calculated with FEMM soft ware [13].Item Modeling of Aerodynamic Forces on the Wind Turbine Blades(Journal of Clean Energy Technologies, 2015) Asif Memon; Saleem R. Samo; Asad, Muhammad; Fareed H. MangiThis research work is aimed to improve the wind turbine modeling for a better representation of aerodynamic forces around the blades. The modeling of forces has been carried out using the actuator surface hybrid model. This model combines the blade element method and Navier-Stokes equation solver. The forces are extracted using real airfoil section of S809 in order to impose on the line which represents the actuator surface. The near wake is calculated and compared with the proposed model and the existing models.Item Mechanical and Microstructural Evaluation of Squeeze Cast Al-4% Cu Alloy Using a Full-Factorial Experimental Design(Journal of Minerals, Metals and Materials, 2014) Haider, Khwaja Mustafa Amin; Mufti, Nadeem AhmadA full factorial design was employed to investigate the effect of squeeze pressure in conjunction with thermal parameters, i.e., melt and die temperatures, on the mechanical properties of a squeeze cast Al-4%Cu alloy. Considerable variations in mechanical properties existed between different test runs, and these were discussed based on cooling rates previously quantified for a squeeze-cast Al-4%Cu alloy. The completeness of a full factorial design not only identified a combination of process parameters for optimum results but also facilitated an evaluation of the minimum pressure required to eliminate porosity and influence the die temperature on the microstructure of the squeeze-cast alloy. In addition to the optimum run, particular importance was given to those runs that had more desirable levels of control factors with respect to energy consumption or tooling life. A microstructural analysis of these runs indicated the possibility of precipitation hardening that can open up further investigations toward the opportunities associated with in situ heat treatment of age-hardening, squeeze cast aluminum alloys.Item Strain energy based homogenization method to find the equivalent orthotropic properties of sandwich structures(SI NDH UNIVERSITY RESEARCH JOURNAL (SCIENCE SERIES), 2014) H. IJAZ; M. ASAD; A. MEMON; K. B. AHMED; H. ABBASI; A. N. LAGHARIThe purpose of present study is to present a methodology to determine the effective elastic properties of sandwich structures. This methodology is based on strain energy based criteria. Sandwich structures contain core material and face sheet. Earlier work in this domain contains the homogenization of core material and determining its equivalent orthotropic properties. The equivalent properties for core material then modeled along with face sheet for final analysis. In the present study however a direct scheme is proposed. Here core material and face sheet are modeled together to determine the equivalent orthotropic properties of sandwich structure.Item Prediction of delamination crack growth in Carbon/Fiber Epoxy composite laminates using non-local interface damage model(Mechanics & Industry, 2014) Hassan ijaz; Muhammad Asad; Gornet, Laurent; Yasir Alam, SyedThe use of composite laminates is increasing in these days due to desired directional properties and low densities in comparison of metals. Delamination is a major source of failure in composite laminates where a crack like entity can initiate and propagate between different layers of composite laminates under given loading conditions. Damage mechanics based theories are employed to simulate the delamination phenomena between composite laminates. These damage models are inherently local and can cause the concentration of stresses around the crack tip. In the present study integral type non-local damage formulation is proposed to avoid the localization problem associated to damage formulation. A comprehensive study is carried out for the selection of different non-local variables. Finite Element simulations based on proposed non-local damage models and classical local damage model are performed and results are compared with available experimental data for UD IMS/924 Carbon/fiber epoxy composite laminate.