Current and Recent Projects
Mechanics of Intraocular Pressure Increase Associated with Genetic Factors
National Science Foundation
Partner: Kellogg Eye Center, Julia Richards Co-PI
The research objective of this project is to use information emerging from glaucoma genetics to inform understanding of the biomechanical processes by which eye pressure is maintained. An interdisciplinary approach combines engineering analyses and molecular genetic tools to study how molecular genetic processes can affect the mechanics problem that leads to elevated eye pressure. The research includes molecular analysis of circulatory fluids from cultured media and donor eyes. Of particular relevance is quantification of myocilin, a protein made by ocular tissues that has been implicated in traits that involve elevated eye pressure. This information will be incorporated in mathematical/computer models to study a key aspect of the eye's circulation system- the interaction of ocular fluid and fine meshwork tissues through which the fluid percolates. The fluid-solid interaction results in forces and pressures that can: (1) alter the tissue's shape and flow and thereby produce increased pressure and (2) provide stimulus to initiate a biological signaling process to alter the flow, and thereby control pressure.
Research on the mechanobiology of ocular tissue and elevated eye pressure has direct application to both ocular hypertension and glaucoma. Ocular hypertension affects about 10% of the population over age 40. Millions of people worldwide eventually develop glaucoma, making it one of the leading causes of irreversible blindness, at great personal and societal costs. The knowledge gained will also be relevant to organs such as the kidney, the liver and the lymphatic system, having mesh-like tissues similar to the trabecular meshwork of the eye.
Ocular Biomechanics
National Science Foundation (REU Awards)
In order to accomplish its function of sight, the eye must also act as a mechanical structure and thereby support and protect its internal components, resist external loads, move, and maintain intraocular pressure. Ocular tissue, like most biological tissues, is difficult to mechanically characterize because of its high compliance, viscoelastic nature and the necessity to maintain biological conditions during the test. Eye tissue's mechanical properties are necessary for biomechanical models of the eye, analysis of impact injury, and the study of certain diseases of a mechanical nature, such as glaucoma and keratoconus. In this research the rate dependent constitutive properties of ocular tissues are being determined in tension, compression and shear, mathematically characterized, and linked to the accurate prediction of the eye's biomechanical response. This refined understanding of the eye's dynamic behavior will lead to improved treatments for certain diseases as well as diagnostic and surgical procedures. The research will also help inform guidelines for ocular damage criteria and the design of protective ocular gear.
Dynamic Response of Rigid, Foamed Biocomposites
Sponsor: National Science Foundation
Microcellular foamed polymers are produced by the use of a decomposing gas in the polymer which leaves behind microcellular voids within stiff, lightweight materials. An objective of the work is to reinforce these materials with plant fibers since such composites have been found to possess highly dissipative, foam-like dynamic response in a rigid, lightweight form. The voids as well as the cellular and vascular anatomy of the natural fibers have been found to play a role in this behavior. The goal of the project is to describe the micro-structural behavior of the biocomposites under dynamic loading, and to connect it to macro-structural response. This knowledge is unavailable for microcellular biocomposites, and will enable the exploitation of the natural properties of the underlying materials and lead to tailored, multi-functional material systems. Building on ideas from polymer crystallization and traditional composites, fundamental research will be conducted concerning micro-structural response, modeling, microscopy, microcellular processing and testing.Potential applications range from impact safety materials in automobiles and municipal transportation systems to infrastructural materials like specialized flooring, guard rails, seismic panels, and composite slabs, and to less obvious ones like electronics protection and biomedical scaffolds. The participation of a potential large scale user of the materials can help lower the cost of the materials and work to overcome the financial inertia that hinders the use of new materials by smaller manufacturers. Many candidate applications are presently met with petroleum-based materials. The replacement of just a moderate amount of these materials with environmentally-friendly alternatives can produce significant environmental benefit.
Impact Response and Failure of Bio-Composites
Sponsor: National Science Foundation
This GOALI project is a collaboration with Ford Motor Company on the mechanical impact performance and energy absorption capabilities of composite materials formulated from natural fibers embedded in synthetic and natural polymeric binding resins. The goal is to develop understanding of the energy dissipation and failure mechanisms of these bio-composites at the micromechanical level, for the purpose of increasing their use in impact safety applications. Various natural materials will be treated in the research including bast, prairie grass and cellulose fibers, and soy based resin. Composite formulations of the materials will be manufactured and laboratory tested to determine their mechanical response and fracture characteristics when impacted at high rate. Based on the test results and scanning electron microscopy of test samples, a micromechanical finite element model will be developed to investigate the relationships between failure mechanisms, energy dissipation mechanisms, and material design of these bio-composites.The successful completion of the research will yield a general understanding of the impact response and failure behavior of bio-composites, facilitating their design for impact safety applications. These materials could serve as replacements of traditional glass/vinyl ester composites in an increased range of applications, and offset some of the petroleum consumed in the manufacture of the traditional composites. General knowledge will result on high rate measurement techniques, appropriate interpretation of the resulting data, its connection to energy absorbing behavior and micromechanical modeling techniques for impact processes.
Spray Deposited High Damping Shape Memory Alloy Composite Structures
Sponsor: National Science Foundation
The research objective of this grant is to develop a new class of high damping structures having a shape memory metal alloy composite casing over a carbon fiber reinforced polymeric (FRP) composite tube. It is expected that the traditional FRP core will provide the high stiffness while the damping capacity accomplished by the shape memory alloy casing. The research will be conducted in three key segments: (1) developing the fabrication technology (spray forming) for building shape memory alloy casings on the FRP cores, (2) characterizing the stiffness, strength and damping capabilities of the new structures, and (3) integrating the design, manufacture, and field testing of prototype automotive half -shafts.The fabrication technology to be developed as part of this project will introduce a new way of making multi-material, multi-functional structures that cannot be conveniently fabricated by other manufacturing methods. These novel high damping structures would find use in challenging, vibration prone applications in the automotive, aerospace, and cutting tool industries.
Mechanical Behavior of Soy-Based Plastics and Rubber
Sponsor: United States Department of Agriculture
To meet a particular impact safety application, a part must meet three specifications: (1) total energy to be dissipated, (2) maximum stress allowed during the absorption process, and (3) minimum dynamic failure stress. These specifications necessitate that a material have low rate hardening, moderate stiffness, gradually increasing flow stress, and sufficient overall strength. To determine these properties, the material must be dynamically tested to failure at various loading rates. Testing apparatus' and protocols have been developed in our laboratory to determine these properties for low impedance materials used for impact safety such as foams, foamed plastic, rubber and thermoplastics. This project is concerned with the use of soy materials in SMC, thermoplastics (TPO, TPE and TPV) and rubber. Soy will be incorporated in the thermoplastics in the form of polyol and oil, and as fillers- including hulls, meal and flour. In SMC, soy thermosetting resin will be used, as well as soy fillers. The applied research work will be tuned toward applications related to energy absorption, and intends to build on preliminary work that shows energy dissipation properties of specimens including soy can be equal or better than control specimens lacking soy.
Soy Foams for Automotive Applications
Sponsor: United States Department of Agriculture
The purpose of the project is to pursue the use of soy based foams for automotive NVH and impact applications. Of interest are rigid and flexible foams of soy blended polyol resins, some containing soy meal and flour fillers. Foams are conventionally difficult to dynamically characterize due to their softness and post crush stiffening as bubbles collapse. In preliminary research using various rigid soy foam formulations, a successful test procedure has been developed for characterizing foams for impact. Also, previous tests on filled biomaterials indicate they generally possess low dependence on loading rate and fail in a progressive manner (rather than abruptly). Both these characteristics are beneficial for impact energy dissipation. The project includes rate dependent testing of foams as well as finite element models of the impact process incorporating the test data.
High Strain Rate Properties of Plastics
Sponsor: Ford Motor Company
The rate dependence of the mechanical properties of plastic and other low-impedance materials is notoriously difficult to determine because of the low forces that occur during the test coupled with response rates on the order of impact events. In this project laboratory and computational methods have been developed for measuring and predicting the high rate response of this class of materials.
Modeling of Ultrasonic Joining of Thick Plate Structures
Sponsor: NIST and Ford Motor Company
Ultrasonic metal welding is a joining method in which ultrasonic energy is used to bond two pieces of metal together. High frequency motion is applied via a "sonotrode" tip to the metal pieces while they are held under a clamping force. The resultant scrubbing motion between the two pieces removes surface oxides, and thereby, inter-atomic contact and mechanical mixing of the metal occurs, , although the exact bonding mechanism is not perfectly understood. Since ultrasonic welding can rapidly join metallic materials cleanly and consumes less energy compared to conventional welding methods, it has attracted interest in recent years as an industrial joining method. In order to understand the process better, thermo-mechanical analysis of ultrasonic spot welding has been performed using finite element models. The computation yields temperature time histories of aluminum specimens during welding that can be used to predict welding behavior, select welding parameters, and design welding machinery. The results have been validated by physical tests.
Alan Argento
