Constrained Nonlinear Model Predictive Control of an MMA Polymerization Process via Evolutionary Optimization

In this work, a nonlinear model predictive controller is developed for a batch polymerization process. The physical model of the process is parameterized along a desired trajectory resulting in a trajectory linearized piecewise model (a multiple linear model bank) and the parameters are identified for an experimental polymerization reactor. Then, a multiple model adaptive predictive controller is designed for thermal trajectory tracking of the MMA polymerization. The input control signal to the process is constrained by the maximum thermal power provided by the heaters. The constrained optimization in the model predictive controller is solved via genetic algorithms to minimize a DMC cost function in each sampling interval.Comment: 12 pages, 9 figures, 28 reference

A predictive model for failure properties of thermoset resins

A predictive model for the three-dimensional failure behavior of engineering polymers has been developed in a recent NASA-sponsored research program. This model acknowledges the underlying molecular deformation mechanisms and thus accounts for the effects of different chemical compositions, crosslink density, functionality of the curing agent, etc., on the complete nonlinear stress-strain response including yield. The material parameters required by the model can be determined from test-tube quantities of a new resin in only a few days. Thus, we can obtain a first-order prediction of the applicability of a new resin for an advanced aerospace application without synthesizing the large quantities of material needed for failure testing. This technology will effect order-of-magnitude reductions in the time and expense required to develop new engineering polymers

Modelling the forming mechanics of engineering fabrics using a mutually constrained pantographic beam and membrane mesh

A method of combining 1-d and 2-d structural finite elements to capture the fundamental mechanical properties of engineering fabrics subject to finite strains is introduced. A mutually constrained pantographic beam and membrane mesh is presented and simple homogenisation theory is developed to relate the macro-scale properties of the mesh to the properties of the elements within the mesh. The theory shows that each of the macro-scale properties of the mesh can be independently controlled. An investigation into the performance of the technique is conducted using tensile, cantilever bending and uniaxial bias extension shear simulations. The simulations are first used to verify the accuracy of the homogenisation theory and then used to demonstrate the ability of the modelling approach in accurately predicting the shear force, shear kinematics and out-of-plane wrinkling behaviour of engineering fabrics

A Government/Industry Summary of the Design Analysis Methods for Vibrations (DAMVIBS) Program

The NASA Langley Research Center in 1984 initiated a rotorcraft structural dynamics program, designated DAMVIBS (Design Analysis Methods for VIBrationS), with the objective of establishing the technology base needed by the rotorcraft industry for developing an advanced finite-element-based dynamics design analysis capability for vibrations. An assessment of the program showed that the DAMVIBS Program has resulted in notable technical achievements and major changes in industrial design practice, all of which have significantly advanced the industry's capability to use and rely on finite-element-based dynamics analyses during the design process

Experimental and numerical studies on forming and failure of woven thermoplastic composites

Fuel efficiency, weight reduction, and sustainability are major global challenges fuelling research into advanced material systems. There is an urgent necessity to manufacture light weight products from highly recyclable, lightweight materials. Woven thermoplastic composites are attractive light weight candidates for the replacement of metallic parts in a wide range of industries from automotive to aerospace. They offer attractive benefits such as high specific strength, balanced thermomechanical properties, improved fatigue and wear resistance, and recyclability. However, there are two major concerns needed to be addressed properly before they can be adopted into mainstream manufacturing industries: forming and failure. This thesis investigates formability and failure behaviour of a woven self-reinforced polypropylene composite (SRPP) using a custom-built press, an open die configuration, and a real time 3D photogrammetry measurement system (ARAMIS). Specimens with novel geometries having different aspect ratios and fibre orientations were formed until catastrophic failure. Deformations and strains were measured to construct a strain-based path dependant failure envelope in a principal strain space. Optical microscopy investigations were conducted to reveal the relation between incorporated failure mechanisms and deformation modes of the composite. Then, experimental forming and failure behaviours of SRPP were benchmarked against a woven glass-fibre reinforced polypropylene composite (GRPP). Characterisation experiments were conducted on SRPP composite using a universal testing machine and a real time strain measurement system to elucidate mechanical behaviours of the composite at room temperature. The highly nonlinear behaviour of SRPP necessitated adopting an incremental deformation theory to develop constitutive stress-strain relations and construct an orthotropic material model. Material and failure models were coded in FORTRAN and implemented into a finite element analysis using the Abaqus-Implicit solver. A finite element model with a nonlinear contact condition was developed to predict formability and failure behaviours of the SRPP during stamp forming process. Comparison between experimental and finite element analysis results proved high accuracy and reliability of the developed numerical model in predicting formability and failure of a woven self-reinforced polypropylene composite. The finite element analysis predictions demonstrated the potential of the developed numerical model to accurately predict strain path, evolution of surface strains, and failure initiation in woven composites. Finally, wrinkling behaviour of the SRPP composite was investigated through a novel Modified Yoshida Buckling Test (MYBT). The inadequacy of the current wrinkling measures to predict compressive instability in woven composites was shown. A more reliable, wrinkling-sensitive criterion, based on gradient of principal strains, was proposed. An important conclusion drawn from this study indicates that proper selection of forming path, fibre orientation and specimen dimensions facilitates manufacturing complex parts from woven thermoplastic composites. The developed numerical model showed the potential to predict failure of the thermoplastic composites experiencing complicated loading conditions. This process eliminates the need to conduct expensive, time consuming trial and error manufacturing processes to achieve flawless products made of woven thermoplastic composites

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences