Sponsored by: Jt. EPD/MDMD Synthesis, Control and Analysis in Materials Processing
Program Organizer: Anand J. Paul, Concurrent Technologies Corporation, 1450 Scalp Avenue Johnstown, PA 15904
Wednesday, PM Room: B1
February 7, 1996 Location: Anaheim Convention Center
Session Chairperson: Anand J. Paul, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904
8:30 am
MICROSTRUCTURE PATH PLANNING DURING CONSOLIDATION OF TITANIUM METAL MATRIX COMPOSITES: Ravi Vancheeswaran, David G. Meyer, Haydn N.G. Wadley, IPM Laboratory, School of Engineering and Applied Science, Charlottesville, VA 22903
The consolidation of fiber reinforced metal matrix composites is a key step in the processing of high performance composite systems. A simulation tool has recently been developed for predicting the evolution of the composites internal state microstructural variables (like relative density, fiber microbending/fracture, and chemical reaction layer thickness at the fiber-matrix interface) during consolidation processing. Here, a Generalized Predictive Control (GPC) scheme is used in conjunction with the simulation tool to design process paths that minimize fiber damage and the reaction product thickness while simultaneously maximizing the composites relative density. The microstructural evolution depends nonlinearly on the process conditions and therefore the scheme uses a constantly updated linearization of the model to optimize the input process variable vector. A control simulation is presented to illustrate the performance of the control scheme and to assess the feasibility of its use for the achievement of goal state microstructures at the completion of consolidation cycles. Electrical and Computer Engineering Dept., University of Colorado, Boulder, CO 80309-0425.
8:55 am
MICROSTRUCTURE TRAJECTORY OPTIMIZATION DURING CONSOLIDATION OF POROUS TITANIUM MATRIX COMPOSITE MONOTAPES: R. Vancheeswaran, R. Gampala, H. N. G. Wadley, School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22903
The high temperature consolidation of fiber reinforced titanium matrix composites (TMC's) seeks to reduce the concentration of matrix pores (i.e., increase relative density), while simultaneously minimizing fiber microbending/fracture, and the thickness of reaction products and the fiber-matrix interface. These three "microstructure" goals have conflicting dependencies upon the consolidation processes variables (time varying temperature and pressure) and it has been difficult to identify process pathways by "trial and error" that lead to composites of acceptable microstructure. The availability of high performance computers, powerful non-linear programming tools and experimentally validated unified dynamic consolidation models have paved the way for finding a "globally optimal" trajectory of process variables that will eliminate porosity, limit both fiber damage and reaction product thickness while minimizing the processing time.
9:20 am
METAL MATRIX COMPOSITE MONOTAPE DENSIFICATION DUE TO COMBINED CREEP AND PLASTICITY OF ASPERITES: R. Gampala, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904; R. Vancheeswaran, H.N.G. Wadley, School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22903
Previous models of the consolidation of metal matrix composite monotapes have been based upon micromechanical analysis of contact deformation by rate independent plasticity and power law creep (i.e. steady state creep). These models have recently been utilized to simulate and optimize consolidation process cycles so that they steer the MMC microstructure to a user defined goal state. However, the instantaneous response of the plasticity mechanism caused finite discontinuities in the state vector field and thus the large body of results for trajectory optimization schemes that required continuous vector fields could not be utilized. To overcome this problem, a unified creep/plasticity constitutive model is used to derive the contact deformations for monotape consolidation. The contact blunting of a hemispherical asperity is first analyzed and its response represented by relating (i) the contact area to the blunting strain and (ii) the mean contact pressure to the blunting rate. This unified blunting problem is than numerically solved using finite element analysis, and results presented for two composite systems of interest (Ti-24Al-11Nb/SCS-6 and Ti-6Al-4V/SCS-6). The resulting model is amenable to the application of non linear programming methods to "globally" optimize the consolidation trajectory.
9:45 am
MULTI-LEVEL SIMULATION OF BRIDGMAN GROWTH OF [[beta]]-NiAl AND CdTe CRYSTALS: Hong Ouyand, Wei Shyy, Department of Aerospace Engineering, Mechanics and Engineering Science, University of Florida, Gainesville, FL 32611
A computational model has been developed for the Bridgman growth processes of [[beta]]-NiAl and CdTe crystals. The model accounts for heat transfer around the heater and the ampoule, and phase change dynamics. To handle the geometrical and physical complexities of the crystal growth processes, a two-level approach has been developed. At the global furnace level, combined convection/conduction/radiation calculations with realistic geometrical and thermal boundary conditions supplied by the global furnace simulations. The present multi-level model can help improve the predictive capabilities for crystal growth techniques by optimizing the use of the computing resources; it allows one to probe the effects of different physical and geometrical variables on the crystal quality.
10:10 am
COMPUTATION OF MAGNETICALLY SUPPORTED FREE SURFACE BY A COUPLED FINITE/BOUNDARY ELEMENT METHOD: S. S. Ping, B. Q. Li, Dept. of Mechanical Engineering, Louisiana State University, Baton Rouge, LA 70803
A computational methodology based on the coupled finite element and boundary/element methods is presented for predicting the free surface shapes of liquid droplets and cylinders supported by the electromagnetic field. This is an extension of our previous FE/BE model for induction calculations. The free surface algorithm is developed based on the weighted residual method, the same that forms as a basis for nonlinear finite element formation. The computational scheme is iterative but robust and efficient and is capable to simulating complex shape deformations. Detailed algorithms will be given. Computational results are presented for magnetic levitation under both normal and microgravity conditions and compared with available experimental measurements.
10:35 BREAK
10:45 am
CONCURRENT ENGINEERING OF DIE CASTING PROCESS PARAMETERS AND TOOLING: Yong K. Park, Paul Paliani, Jerald Brevick, Dept. of Industrial Welding and Systems Engineering, The Ohio State Univeristy, Room 210, Baker Systems Building, 1971 Neil Avenue, Columbus, OH 43210
The horizontal cold chamber die casting process can produce a wide range of near-net shape, non-ferrous castings with small dimensional variation, excellent surface finish and very complex geometries. However, top quality die casting can be achieved only when optimal performance of the cold chamber and plunger is maintained during the molten injection phase of the process. Cold chambers (shot sleeves) are known to deteriorate fast and sometimes fail catastrophically because of poor design. Thermoelastic distortion and catastrophic fracture are leading causes to degrade quality, increase downtime and thereby decrease productivity/profitability. Therefore, a systematic approach to minimize irregular, adverse conditions which prevent an optimal injection profile, is highly desirable. To eliminate them, design criteria for shot sleeves (mechanical and thermal) were developed using analytical tools, numerical process simulation and physical elements. Also, the relationship between die casting process parameters and deterioration/failure mechanisms were carefully evaluated.
11:10 am
DEEP DRAWING OF CONICAL FRUSTUM SHAPED CUPS - A COMPUTER SIMULATION: Ch. A. V. Prasad, R. C. Chaturvedi, Dept. of Mechanical Engineering, Indian Institute of Technology, Bombay 400076, India
The authors have developed a theory of deep drawing of conical frustum shaped cups. This theory has been used in the development of a dedicated software for modeling the process. The software developed provides full information on the state of stress and strain throughout the formed sheet at successive stages of forming under a specified conditions of processing. It also provides a graphical display of the progress of the forming process. Different modules of the software such as those for input of geometry, tools, process, and material parameters, and calculations of geometry, forces, stresses, and strains at different stages of the process are described along with those for graphical display of the forming process and for displaying the results. The paper also gives the validation procedure used and sample outputs showing the influence of some of the process parameters on the formability of such shapes.
11:35 am
ANALYSIS OF THERMAL SPRAY SYSTEMS BY COMPREHENSIVE NUMERICAL SIMULATIONS: Xiaolong Yang, Shmuel Eidelman, Science Applications International Corporation, 1710 Goodridge Drive, McLean, VA 22102
A comprehensive numerical capability for the analysis of Thermal Spray (TS) systems consisting of a three-dimensional compressible, turbulent flow Navier-Stokes model and a multi-phase particle flow model in Lagrangian formulation, was developed. This capability is validated for a set of flow conditions typical for TS. The developed methodology is used for analysis of the JP-5000 TS gun gas and coating powder flow conditions. Modeling and analysis of particle/turbulent eddies interaction is performed. The simulations allow evaluation of particle density, velocity, and temperature distribution in the TS gun's flow field and optimization of these parameters for particular coating conditions. This methodology can be used for process control and reliability improvement, and has the potential to significantly improve TS gun performance through control of its parameters.
12:00 pm
COMPUTER MODELS FOR ROLLING, BENDING, AND FORGING OF SINGLE CRYSTAL SUPERALLOYS: D. Zhao, S. Cheng, R. Thomas, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904
Single crystal superalloys have long been used in cast form to make gas
turbine engine components. However, the possibility of hot forming cast single
crystal superalloys has been ignored for the most part because of their low
ductility. Successful forming of single crystals would open other areas of
application in aerospace, marine and land based powder generation. Forming of
single crystals could provide single crystal sheets for applications such as
combustor components. Furthermore, larger components could be fabricated out of
single crystal superalloys using these enhanced technologies, opening up the
possibility of their use in more powerful combustors. The hot forming
technologies for single crystals which are being developed include hot rolling,
bending and forging. To significantly shorten the time between the development
of optimized manufacturing routes and their implementation on the shop floor,
computer modeling was performed for these fabrication processes as applied to
gas turbine engine components. Modeling of forming processes was closely
integrated with materials testing. The results of computer modeling, materials
testing, and laboratory scale trial runs are presented.
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