Eric D. Haugse

Multidimensional strain field measurements using fiber optic grating sensors

Fiber optic grating sensors written into polarization preserving optical fiber may be used to monitor multidimensional strain fields in composite materials. This paper provides an overview of the characterization and test of multiaxis fiber grating sensors formed by writing 1300 and 1550 nm fiber gratings into polarization preserving optical fiber. A discussion of the usage of these multiaxis fiber grating sensors to measure two and three dimensional strain fields will be made. A brief review of practical applications of the technology to measure shear strain, transverse strain gradients as well as axial and traverse strain will be made with emphasis on aerospace and civil structure applications.

Structural health management for aging aircraft

An effective structural health management (SHM) system can be a useful tool for making aircraft fleet management decisions ranging from individual aircraft maintenance scheduling and usage restrictions to fleet rotation strategies. This paper discusses the end-user requirements for the elements and architecture of an effective SHM system for application to both military and commercial aging aircraft fleets. The elements discussed include the sensor systems for monitoring and characterizing the health of the structure, data processing methods for interpreting sensor data and converting it into useable information, and automated methods for erroneous data detection, data archiving and information dissemination. Current and past SHM technology development/maturation efforts in these areas at the Boeing Company will be described. An evolutionary technology development strategy is developed in which the technologies needed will be matured, integrated into a vehicle health management system, and benefits established without requiring extensive changes to the end-users existing operation and maintenance infrastructure. Issues regarding the end-user customer acceptance of SHM systems are discussed and summarized.

Crack Growth Detection and Monitoring using Broadband Acoustic Emission Techniques

This paper will provide an overview of an approach that will autonomously detect and monitor crack growth in aircraft structure. Present day computer technologies make it possible to put a small computer and sensor system on an aircraft to monitor structural health at locations that are difficult and costly to inspect through more traditional techniques. The health of the monitored locations can be determined by the end user through normal operations, thereby providing a significant reduction in scheduled maintenance requirements. All types of aircraft suffer from structural cracking. Even though the location of the crack can often be predicted, the inspections required are costly, often requiring significant structural disassembly. Sometimes there is an unacceptable level of uncertainty in NDI results, leading to more frequent inspections and even greater costs due to prematurely replaced structure. Broadband Acoustic Emission (BAE) systems have demonstrated the capability to detect crack growth in structure. Such a system can autonomously monitor aircraft structure during operation and provide information necessary to detect crack growth, determine the source location and monitor crack growth without disassembly. This paper will present an overview of the BAE approach to crack monitoring. Results from proof-of-concept testing will be included with comparisons to BAE waveform analysis results. Conclusions, system requirements and a preliminary design of the electronics and software necessary for an aircraft crack monitoring flight, system will also be presented.

Transversely loaded fiber optic grating strain sensors for aerospace applications

Most fiber grating sensor technology that has been developed to support strain sensing involves the measurement of axial strain. Fiber grating sensors are however capable of monitoring transverse as well as axial strain. This paper reviews a series of applications of this technology that are of particular interest to aerospace applications.

Durability patch and damage dosimeter: a portable battery-powered data acquisition computer and durability patch design process

Repairs of secondary structure can be accomplished by restoring structural integrity at the damaged area and increasing the structures damping in the repair region. Increased damping leads to a reduction in resonant response and a repair that will survive for the life of the aircraft. In order to design a repair with effective damping properties, the in-service structural strains and temperatures must be known. A rugged, small and lightweight data acquisition unit called the Damage Dosimeter has been developed to accomplish this task with minimal impact to the aircraft system. Running autonomously off of battery power, the Damage Dosimeter measures three channels of strain at sample rates as high as 15 kilo-samples per second and a single channel of temperature. It merges the functionality of both analog signal conditioning and a digital single board computer on one 3.5 by 5 inch card. The Damage Dosimeter allows an engineer to easily instrument an in-service aircraft to assess the structural response characteristics necessary to properly select damping materials. This information in conjunction with analysis and design procedures can be used to design a repair with optimum effectiveness. This paper will present the motivation behind the development of the Damage Dosimeter along with an overview of its functional capabilities and design. In-service flight data and analysis results will be discussed for two applications. The paper will also describe how the Damage Dosimeter is used to enable the Durability Patch design process.