Charles Keilers

Bio: Charles Keilers is an academic researcher from Stanford University. The author has contributed to research in topics: Finite element method & Delamination. The author has an hindex of 4, co-authored 4 publications receiving 533 citations.

Finite element analysis of composite structures containing distributed piezoceramic sensors and actuators

Abstract: A finite element formulation is presented for modeling the dynamic as well as static response of laminated composites containing distributed piezoelectric ceramics subjected to both mechanical and electrical loadings. The formulation was derived from the variational principle with consideration for both the total potential energy of the structures and the electrical potential energy of the piezoceramics. An eight-node three-dimensional composite brick element was implemented for the analysis, and three-dimensional incompatible modes were introduced to take into account the global bending behavior resulting from the local deformations of the piezoceramics. Experiments were also conducted to verify the analysis and the computer simulations. Overall, the comparisons between the predictions and the data agreed fairly well. Numerical examples were also generated by coupling the analysis with simple control algorithms to control actively the response of the integrated structures in a closed loop.

Analysis of Laminated Composites Containing Distributed Piezoelectric Ceramics

Abstract: A finite element formulation was developed for modeling the dynamic as well as static response of laminated composites containing distributed piezoelectric ceram ics subjected to both mechanical and electrical loadings. The formulation was derived from the variational principle with consideration for both the total potential energy of the structures and the electrical potential energy of the piezoceramics. An eight-node three- dimensional composite brick element was implemented for the analysis, and three- dimensional incompatible modes were introduced to take into account the global bending behavior resulting from the local deformations of the piezoceramics. Experiments were also conducted to verify the analysis and the computer simulations. werall, the compari sons between the predictions and the data agreed fairly well.

Damage detection and diagnosis of composites using built-in piezoceramics

Abstract: An investigation was performed to develop a technique for using built-in piezoelectrics to detect delaminations and to estimate their size and location in laminated composite structures. Both experimental and analytical work were conducted in the study. Piezoceramics were utilized as sensors for receiving signals and as actuators for dispatching diagnostic waves. A diagnostic technique was developed which combines an electromechanical structural model with an iterative damage identification algorithm to form a closed loop. The structural model was used to predict the frequency response of normal and delaminated structures excited by actuators. The identification algorithm compares the calculation with the data to find a best estimate of delamination size and location. The technique first compares the measured dynamic response to a baseline. If they disagree, the technique searches through the possible locations and sizes of delaminations using the structural model and compares the results with the measurements. The loop terminates when the calculated and the measured frequency responses agree. Tests on composite beams with implanted delaminations were conducted to verify the model and predictions. Overall, the predictions agreed with the data.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Impact damage detection in composite structures using distributed piezoceramics

Abstract: In this presentation, a concept of a damage diagnostic system using distributed built-in piezoelectric~ for detecting foreign object impact as well as estimating the resulting impact damage is proposed. Based on the concept, an impact detection method has been developed for predicting impact load and impact location for beams. A delamination identification method will also be demonstrated for estimating the location and size of an embedded delamination in composite beams. The impact detection method uses a quadratic fitting method based on transient dynamic response measured from piezoelectric sensors for detecting foreign object impact. The delamination identification method compares measured amplitude response of a structure excited locally by piezo-actuators with estimated measurements to identify the delamination size and location. By combining the two methods, it is possible to develop a damage diagnostic system for structures which may be susceptible to foreign object impact.

Coupled Electro-Mechanical Analysis of Adaptive Material Systems — Determination of the Actuator Power Consumption and System Energy Transfer:

Abstract: This article presents a coupled electro-mechanical analysis of piezoelectric ceramic (PZT) actuators integrated in mechanical systems to determine the actuator power consumption and energy transfer in the electro-mechanical systems. For a material system with integrated PZT actua tors, the power consumed by the PZT actuators consists of two parts: the energy used to drive the system, which is dissipated in terms of heat as a result of the structural damping, and energy dissi pated by the PZT actuators themselves because of their dielectric loss and internal damping. The coupled analysis presented herein uses a simple model, a PZT actuator-driven one-degree-of- freedom spring-mass-damper system, to illustrate the methodology used to determine the actuator power consumption and energy flow in the coupled electro-mechanical systems. This method can be applied to more complicated mechanical structures or systems, such as a fluid-loaded shell for active structural acoustic control. The determination of the act...

Intelligent structures for aerospace - A technology overview and assessment

Abstract: HIS article presents an overview and assessment of the technology leading to the development of intelligent structures. Intelligent structures are those which incorporate actuators and sensors that are highly integrated into the structure and have structural functionality, as well as highly integrated control logic, signal conditioning, and power amplification electronics. Such actuating, sensing, and signal processing elements are incorporated into a structure for the purpose of influencing its states or characteristics, be they mechanical, thermal, optical, chemical, electrical, or magnetic. For example, a mechanically intelligent structure is capable of altering both its mechanical states (its position or velocity) or its mechanical characteristics (its stiffness or damping). An optically intelligent structure could, for example, change color to match its background.17 Definition of Intelligent Structures Intelligent structures are a subset of a much larger field of research, as shown in Fig. I.123 Those structures which have actuators distributed throughout are defined as adaptive or, alternatively, actuated. Classical examples of such mechanically adaptive structures are conventional aircraft wings with articulated leading- and trailing-edge control surfaces and robotic systems with articulated manipulators and end effectors. More advanced examples currently in research include highly articulated adaptive space cranes. Structures which have sensors distributed throughout are a subset referred to as sensory. These structures have sensors which might detect displacements, strains or other mechanical states or properties, electromagnetic states or properties, temperature or heat flow, or the presence or accumulation of damage. Applications of this technology might include damage detection in long life structures, or embedded or conformal RF antennas within a structure. The overlap structures which contain both actuators and sensors (implicitly linked by closed-loop control) are referred to as controlled structures. Any structure whose properties or states can be influenced by the presence of a closed-loop control system is included in this category. A subset of controlled structures are active structures, distinguished from controlled structures by highly distributed actuators which have structural functionality and are part of the load bearing system.