This research focuses on developing an embedded sensor system to monitor the health of a composite rotor component. To support this objective, simulations were developed to investigate the impact of sensor insertions on local structural micro-mechanics and sensor responses. In particular, the potential side-effects (e.g., delamination onset and growth) of imbedding lead zirconate titanate (PZT) piezoelectric sensors in composite structures were studied. A modeling approach for evaluating interlaminar damage under the influence of embedded PZT sensors is proposed. The approach uses finite element cohesive zone models to describe interlaminar damage between plies or at ply ends. In addition, an embedded multi-ply PZT model was developed and integrated with the damage models. The approach presented in this paper analyzes the propagation of interlaminar damage in the vicinity of sensors and quantifies the effect of sensor presence on damage growth. A parametric study was performed to understand how damage zones, the size and geometry of resin pockets, and the locations and properties of PZT sensors affected interfacial strength. Damage behavior, under the influence of an embedded PZT sensor, was examined in specimens having a configuration similar to that of a selected rotating rotorcraft component. Finally, optimal locations of embedded PZT transducers were determined for the specimen under consideration.
Aiming at understanding the structural integrity of two representative concentrating photovoltaic (CPV) module configurations, finite element thermal stress analysis is carried out in this investigation. This study covers the nominal and extreme operating conditions, including system startup and shutdown. While the first CPV module is bonded by epoxy-type material, the bonding material for the second CPV module is lead-free solder. The analysis of the first module confirms that this CPV module can endure the thermal stress under steady-state operation. However, residual stress analysis shows that the epoxy holding together the PV cell/aluminum nitride and aluminum nitride/heat sink pairs will likely break, first at some sporadic spots, and then in a good part of the bond causing the failure of the CPV module, as the cell temperature drops from 100°Cto0°C. Nonlinear viscoplastic analysis using the temperature profile of CPV cell fatigue test ongoing at United Technologies Research Center (UTRC) is performed to evaluate the structure strength and subsequently predict the life of the second CPV module. The result reveals that the maximum characteristic stresses of the PV cell components and heat sink are below the strength allowable for the corresponding materials under both the steady-state and overnight idle conditions. Critical locations on the solder that are potentially susceptible to structural failure after a few thousand thermal cycles due to the excessive shear stress are identified. A rough estimation of the module life is provided and compared with the fatigue test. This investigation provides firsthand understanding of the structural integrity of CPV modules and is thus beneficial for the solar energy community.
An integrated sensor system that continuously monitors the structural integrity of an aircraft’s critical composite components can have a high payoff by reducing risks, costs, inspections, and unscheduled maintenance, while increasing safety. Hybrid sensor networks combine or fuse different types of sensors. Optimal sensor fusion tries to find the optimal number and location of different types of sensors such that their combined probability of detection is maximized. Optimal hybrid sensor networks can be more robust, more accurate, and/or cheaper than networks consisting only of homogeneous sensors. A generic sensor fusion approach that combines the probabilities of detection of heterogeneous sensors is described. A fast greedy optimization approach that provides approximate solutions is described and demonstrated. Computable lower and upper bounds of a probability of detection objective function were determined. Fiber Bragg grating sensors can be inserted in layers of composite structures to provide local damage detection, while surface-mounted piezoelectric lead zirconate titanate sensors can provide global damage detection for the host structure under consideration. The generic approach is demonstrated on such combinations of fiber Bragg grating and lead zirconate titanate sensor networks. It is demonstrated that the proposed approach can be used to answer structural health monitoring network design problems such as the following: (1) Given a number of sensors, what is the maximum probability of detection that the sensors can attain and where should they be positioned to provide the maximum probability of detection? (2) If a given probability of detection is desired, the minimum number, types, and locations of sensors that are needed to attain this probability of detection can be determined. The approach is generic, that is, it can be extended to any number or types of sensors for which probabilities of detection can be defined.
A complex structural assembly often includes components made of isotropic and anisotropic materials and includes components with complex connections such as bolted, riveted, welded, and sliding joints. This paper categorizes the connections into two types, compatible and incompatible interfaces, and their mathematical descriptions are presented. A substructure with composite plate/shell element is provided. An approach, incorporating substructure-component mode synthesis, considering compatible and incompatible interfaces and being capable of handling laminated composite plate/shell (SCMSCIC) is proposed. Coupling equations including laminated composite substructure and including different types of connections between substructures are developed. Examples have shown good agreement from SCMSCIC and entire structure analysis.
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