Staff members at Los Alamos National Laboratory (LANL) produced a summary of the structural health monitoring literature in 1995. This presentation will summarize the outcome of an updated review covering the years 1996 2001. The updated review follows the LANL statistical pattern recognition paradigm for SHM, which addresses four topics: 1. Operational Evaluation; 2. Data Acquisition and Cleansing; 3. Feature Extraction; and 4. Statistical Modeling for Feature Discrimination. The literature has been reviewed based on how a particular study addresses these four topics. A significant observation from this review is that although there are many more SHM studies being reported, the investigators, in general, have not yet fully embraced the well-developed tools from statistical pattern recognition. As such, the discrimination procedures employed are often lacking the appropriate rigor necessary for this technology to evolve beyond demonstration problems carried out in laboratory setting.

A review of structural health monitoring literature 1996-2001

Guided Lamb waves for identification of damage in composite structures: A review

Structural health monitoring (SHM) is being widely evaluated by the aerospace industry as a method to improve the safety and reliability of aircraft structures and also reduce operational cost. Built-in sensor networks on an aircraft structure can provide crucial information regarding the condition, damage state and/or service environment of the structure. Among the various types of transducers used for SHM, piezoelectric materials are widely used because they can be employed as either actuators or sensors due to their piezoelectric effect and vice versa. This paper provides a brief overview of piezoelectric transducer-based SHM system technology developed for aircraft applications in the past two decades. The requirements for practical implementation and use of structural health monitoring systems in aircraft application are then introduced. State-of-the-art techniques for solving some practical issues, such as sensor network integration, scalability to large structures, reliability and effect of environmental conditions, robust damage detection and quantification are discussed. Development trend of SHM technology is also discussed.

Piezoelectric Transducer-Based Structural Health Monitoring for Aircraft Applications.

An inverse method based on a system-identification technique for identifying impact events on a complex structure with built-in sensors is presented. The method using the transfer functions in the system-identification technique identifies the location and force time history of an impact event on a structure without the need of constructing a full- scale accurate structural model or of acquiring excessive training data on the structure, such as neural-network techniques. The system transfer functions for the entire structure are constructed by two sequential procedures: 1) limited impact tests at selected points to establish the system transfer functions from the selected points to a sensor on the structure and 2) an interpolation function approach based on a linear finite element to approximate the system transfer functions from a point inside four neighboring selected points to the sensor. Comprehensive tests with various impact situations verified the accuracy of load and position predictions by the proposed method.

Monitoring Impact Events Using a System-Identification Method

Impacts can inflict serious damage on composite structures. For structures on the surface of an aircraft this has potentially critical consequences. The problem is exacerbated by the fact that the damage is internal, with little or no indication on the surface of the structure, making it difficult to detect. A potential solution to the problem would be an impact monitoring system that could detect when an impact occurred. This idea was explored using a composite panel, inside which a SMART Layer was embedded. Two techniques were studied that were able to estimate the locations of impacts on the panel from the measurements provided by the piezoelectric strain sensors in the SMART Layer. The first technique employed artificial neural networks and the second used a triangulation procedure incorporating a genetic algorithm. The knowledge acquired during the study made it possible to develop a simple and efficient prototype impact monitoring system for the composite panel.

http://iopscience.iop.org/article/10.1088/0964-1726/14/1/027/pdf

An automatic impact monitor for a composite panel employing smart sensor technology

This paper summarizes the theory used in a system that identifies foreign body impact on a composite plate using built-in strain sensors. The identification system consists of a model of the composite plate and an identification algorithm. The algorithm compares the measured response of the plate to the model response and estimates the impact location and force time history. The solution, which uses a smoother/filter optimization, includes a new computational algorithm that saves considerable computation time for systems with many degrees of freedom.

Identifying Impacts in Composite Plates with Piezoelectric Strain Sensors, Part I: Theory

This paper summarizes the implementation of an impact identification system on a composite plate The impact, normal to the surface of the plate, generates a traveling wave that is measured by surface mounted sensors The identification system compares the measured response of the plate to the model response and estimates the impact location and force time history The accuracy and reliability of the system was tested using many impacts distributed across the plate and the robustness of the system was tested by adding simulated noise to the data The system was tested on the composite plate with free boundaries and clamped boundaries The system proved to be accurate with an average location error ranging from 39 inches for the free boundary case to 49 inches for the clamped plate with noise The area monitored by the 13 sensor array was 20 inches by 20 inches

Michael Tracy

Papers

Identifying Impacts in Composite Plates with Piezoelectric Strain Sensors, Part I: Theory

Identifying Impacts in Composite Plates with Piezoelectric Strain Sensors, Part II: Experiment