Raghu Echempati

Dynamic analysis and damping of composite structures embedded with viscoelastic layers

Abstract In recent years, it has been found that composites co-cured with viscoelastic materials can enhance the damping capacity of a composite structural system with little reduction in stiffness and strength. Because of the anisotropy of the constraining layers, the damping mechanism of co-cured composites is quite different from that of conventional structures with metal constraining layers. This paper presents an analysis of the dynamic properties of multiple damping layer, laminated composite beams with anisotropic stiffness layers, by means of the finite element-based modal strain energy method. ANSYS 4.4A finite element software has been used for this study. The variation of resonance frequencies and modal loss factors of various beam samples with temperature is studied. Some of these results are compared with the closed-form theoretical results of an earlier published work. For obtaining optimium dynamic properties, the effects of different parameters, such as layer orientation angle and compliant layering, are studied. Also, the effect of using a combination of different damping materials in the system for obtaining stable damping properties over a wide temperature range is studied.

Computer-aided torch trajectory generation for automated coating of parts with complex surfaces

The work presented in this paper is concerned with the design and development of an efficient computer software package for off- line programming of robots for spray coating. The developed package (called CA- COATS) allows the spray torch to track a path, maintaining the specified spraying distance and proper orientation relative to the part surface at all points, and thus ensuring uniform coating thickness. This software package is done off- line and is complete in itself, eliminating the need for another computer-aided design database of the base surface (although the package can be made to interface with such a database if so desired). Because the algorithm has no iteration, it is computationally efficient. With minor modifications, this package can also be extended to waterjet coating- removal systems.

A Simple Analytical Model of Laser Bending Process

Laser bending is a process of bending a sheet by the irradiation of laser beam on the surface of the sheet. A number of analytical and numerical methods have been proposed for the estimation of bend angle. A brief review of these methods is presented. A finite element analysis of laser bending process is carried out with ABAQUS package for the purpose of understanding the physics of the laser bending. Afterwards, a simple analytical model is developed to evaluate the bending angle in laser bending of metal sheet. The model is based on the elastic-plastic bending of sheet. It is ascertained from the experimental results available in literature that the model provides reasonably good prediction of bend angle. It is also shown that the model can be used for the quick estimation of yield stress of the material during laser bending process.

Integrated metal forming and vibration analysis of sheet metal parts

Modern software programs are routinely used by industries to study the characteristics of and to reduce the cost of sheet metal parts that are used in automotive and other applications. Virtual simulations that are based on complex math models and state-of-the-art computational tools play a very important role in reducing the high costs associated with prototypes and the time to market the product. Formability studies of a sheet metal part determine if a part is formable by changing the factors that affect its formability. Vibration (or modal) analysis is performed to determine the frequency and mode shapes of the component or the assemblies. A gauge optimization study is performed to determine the optimum gage thickness assigned to components of an assembly while constraining the frequency of specified modes to a desired level. Usually these studies are done separately by different engineering departments in a typical automotive industry. In this paper, a single component from an instrument panel (IP) reinforcement assembly is analyzed by integrating the three different studies mentioned above. It was found that the thickness of the bracket and the coefficient of friction in the stamping process should be kept as low as possible to reduce the chance of splits occurring in the bracket. An optimum thickness for the same bracket as part of an assembly can also be determined using a gauge optimization study so that the assembly was stiff enough while minimizing its mass. Thus, an integrated analysis using simulation tools helps in better design of the parts and subassemblies, which ultimately helps stay in competition to produce quality products.

Design and Analysis of an Example Lathe Spindle

This paper discusses the modeling and analysis of an example medium speed medium precision lathe spindle. This and few other similar topics have been assigned as term projects in an introductory senior undergraduate/graduate level finite element analysis course taught at Kettering University. The experiences and the general feedback from the students of the class show satisfactory organization of the course material that includes modeling and analysis of real life examples.With reference to the specific topic on design of machine tool spindles, it is not a new area, however, it is generally taught at the graduate and research levels. Use of modern computational tools to perform iterative design and analysis calculations of such spindles make the senior undergraduate and/or graduate master students aware of the implications of modeling a real life system using the 1D and 3D finite beam elements and to validate those results by a CAE tool. Final course projects such as this serve as a good learning tool to the graduating engineers. Sample results obtained from various CAE tools such as UG-NX 7.5 are presented in the paper and discussed.Copyright

Design and Analysis of a Car-Truck Stand

In this paper application of an example FEA/CAE tool (Finite Element Analysis/Computer Aid Engineering (Cosmos®) to the design and analysis of a typical car-truck stand used by the railways is discussed. The car-truck stand consisted of several pieces of A-500 steel tube and A36 steel welded together and is used to support one end of a freight car during maintenance operations. Design of experiments via Taguchi method approach was attempted to evaluate the car-truck stand currently used by the rail industry. Experiments were conducted to validate some of the simulation results. In this study, three parameters were evaluated (overall stand height, material thickness, and stand geometry). The Taguchi method consisted of nine experiments. Each of the nine experiments for each structure was evaluated using the CAE tool. Real experiments were also done on the current design of the stand and a static load test was conducted to validate some of the CAE results. The static test was done by fixing strain gages to the car stand and vertically loading the car stand. The output response which was measured is the safety factor determined from the CAE analyses. All resulted are presented in the form of tables and discussed.Copyright

Optimal Central Composite Design for Manufacturing Simulation of 0.50 Caliber Projectile

Design and manufacturing simulations of critical components such as bullets are considered crucial, particularly, when it is associated with the expense and time constraint of the engineering projects. During the manufacturing, the projectile jacket is the component that faces the greatest strain or stress. In order to find an optimal manufacturing operation for the .50 caliber projectile, an experiment is performed using the Box-Wilson Central Composite Design (CCD) using a combination of two controlled factors, i.e., friction coefficients and hardening exponents, with three-levels of each. The sensitivity of the plastic strain to the hardening exponent and friction coefficients is analyzed. The response surface plot fits well to the second-order polynomial function and is able to provide relative the same plots when the model is extended up to the fourth-order. Furthermore, it is found that the greatest plasticity likely to occur in the jacket walls as the ironing process is performed. Based on the residual strain and stresses analysis, it is evident that the selected material used in the production of projectile is viable. Finally, the ductile fracture analysis confirms that the jacket design is considered safe for the selected manufacturing processes.Copyright

Modeling, Forming, Modal Analysis, and Gauge Optimization of Sheet Metal Parts

CAE tools can be used to study the characteristics and reduce the cost of sheet metal parts that are used in products. Using an instrument panel that is used in a car as an example which is made up of sheet metal components the basic process of analyzing the components and assembly to optimize its design is discussed. The paper is mostly educational in the sense that the integrated procedures and analysis presented here can be adapted in a senior level course and at a university that has state-of-the-art CAE tools as discussed in this paper. Several tutorials have been developed that are user-friendly and show how the subsequent analysis can be conducted. To the best of the knowledge of the authors, no such tutorials exist, or are available to students at a university. To start out, solid modeling of the individual sheet metal components using different CAD programs is discussed. Then a discussion on how these solid models can be imported to different CAE programs to be meshed and then subsequently exported to high end solvers like LS-Dyna or MSC Nastran is presented. The integrated analysis that was conducted for this paper was forming analysis of the individual components, followed by modal analysis and gauge optimization of the entire instrument panel assembly. Also, a design of experiments based on Taguchi method is discussed which was done to determine the effects that the input factors have on the results of the forming simulations that were conducted. It is believed that the contents of this paper serve as an educational tool to the students and the instructors involved in understanding and/or teaching sheet metal forming simulation. Sample tutorials will be presented at the conference meeting.Copyright