Sponsored Research Projects
1. Structural response of hybrid ship connections subjected to fatigue loads
Supported by:
Investigators: V. Caccese (PI), S. Vel (co-PI)
Period: 7/2005 – 7/2008
Project Summary:
The overall objective of this project is to quantify the fatigue life of hybrid composite/metallic connections in advanced hull-form structures. In the ocean environment, a ship must be able to survive when exposed to many forms of loading which occur dynamically and repeatedly. Experience has shown that more often than not, structural failures occur at connections and interfaces, and rarely occur in the bulk material sections. Therefore, an in-depth study of fatigue response of hybrid connections is essential to insure that newly emerging hybrid ship design will have a high degree of structural integrity. As part of this research effort, we will develop, analyze and experimentally quantify the fatigue response of hybrid composite/metallic structural systems and hybrid connection concepts for applications that are of relevance to the U.S. Navy. The research will focus on the development of cost effective connection details for hybrid composite/metal connections for flat and curved panels. Guidelines for quantifying the strength, stiffness and fatigue life of hybrid connections through modeling and fatigue testing of bonded, bolted and welded hybrid connections under in-plane, flexure and combined loading will be developed. Damage models that take into account the influence of factors such as adhesive material properties, substrate material properties, bondline thickness, environmental effects, bolt torque and viscoelastic properties on the fatigue strength will be developed and experimentally verified. The research effort will include the development of a methodology for the analysis and multi-objective optimization of the global structural system, skin stiffeners and connection properties using finite element analysis and genetic algorithms. It is expected that the hybrid connection concepts developed and fatigue tested under this research effort will have a broad impact on future Navy vessels.
2. Design of functionally graded materials using transient nonlinear simulations and genetic algorithm optimization
Supported by:
Investigator: S. Vel
Period: 8/2004 – 8/2007
Project Summary:
The objective of this research is to develop a robust methodology for the design of functionally graded materials (FGMs). FGMs are advanced composite materials that are engineered to have a smooth spatial variation of material properties. This is achieved by gradually varying the relative volume fractions and microstructure of the material constituents during fabrication. FGM components typically exhibit smaller stresses and higher factors of safety than discretely bonded monolithic materials. The aim of this research project is to create a unified framework for the simultaneous optimization of structural shape, compositional profile and microstructure of metal/ceramic FGMs that are subjected to time varying thermal and mechanical loads. The proposed technique utilizes a nonlinear elastoplastic model and numerical simulations using a meshless method to accurately analyze candidate designs. A robust multi-objective genetic algorithm will be used to simultaneously optimize structure shape, fractional composition and microstructure of the material. If successful, this project will result in a powerful design tool that could assist engineers and other professionals engaged in the design process with FGMs. It will benefit society by contributing new knowledge regarding the simulation and optimization of FGMs and by reducing the failure of mechanical components. A user-friendly software package implementing the proposed method will be developed and distributed freely on the Internet through the PI's web page. The educational plan will emphasize design as an important element of engineering education by incorporating computer-aided analysis, shape and material optimization to the PI's machine design and composite materials courses.
3. Active vibration suppression of composite structures using piezoelectric shear actuators
Supported by:
Investigators: S. Vel (PI), V. Caccese (Co-PI)
Period: 2/2002-4/2005
Project Summary:
The ability to mitigate the effects of structural vibration of an aerospace vehicle is critical to its design. In complex aerospace transport systems, such as envisioned by NASA, there will be many causes of dynamic excitation ranging from the time variation in external pressure and forces being transmitted from operating equipment. It is imperative that the structural vibration characteristics be properly assessed and excessive vibrations be suppressed so that serious vibration problems are not encountered in operational vehicles, especially ones that are manned. Conventional passive damping systems are large, heavy and unsuitable for lightweight composite structures.
The goal of this project is to develop an active vibration suppression system by using piezoelectric shear actuators and sensors that are embedded within composite structures to actively dampen undesired vibrations. The lightweight active vibration suppression system can dramatically reduce the amount of vibration that the composite structure undergoes by applying a strain to the structure that opposes the dynamically induced strain. The vibration suppressed structure will experience reduced stresses with a quickly damped response.
4. Modular advanced composite hull-form ( MACH ) technology
Supported by:
Investigators: V. Caccese (PI), S. Vel (co-PI), B. Segee, (Co-PI), R Lopez-Anido (Co-PI), M Peterson (Co-PI)
Period: 7/2001– 6/2004
Project Summary:
The overall objective of the proposed program is to develop the University of Maine’s Modular Advanced Composite Hull-forms (MACH) concept, a simple hull construction technique that enables both advanced surface ship and submarine designs. The central motivation of the MACH concept is a desire to break out of the restrictions of conventional hull construction techniques and conventional hull forms. Conventional hull construction techniques have limited the ability to build and maintain the complex shapes required for high speed military support vessels in a cost effective manner. Conventional single-hull construction techniques have also restricted submarines to cylindrical shapes that are difficult and costly to reconfigure for new roles. The core of MACH is a modular system consisting of a metallic frame supporting, and closed by, curved panels. MACH is a hybrid structural system where various components are joined together to take advantage of the beneficial properties of each. Therefore, development of hybrid connection technology is one of the primary goals of this effort. In general, the complex shapes required for advanced ship designs will drive the use of composites in the construction of these panels. The panels can have many forms, from monocoque panels with that simply seal the hull to complex panels containing transducers for structural monitoring and sonar applications. The emphasis of the proposed project is on the development of the panelized construction system with an integrated monitoring system. This system will check for integrity of the panel joints and surrounding structure, monitor critical maintenance indicators, check for hydrodynamic conditions that could lead to structural degradation, monitor vibration, and provide acoustic monitoring
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