Key Engineering Materials Vol. 558

Abstract: This paper proposes a damage assessment methodology for the non-structural elements, especially ceiling elements of a building, utilizing an inspection robot. The developed inspection robot equipped with a wireless camera and data processing function has a capability of providing valuable information for the repair and maintenance decision making of a damaged structure. The inspection robots will be able to estimate the damage condition without any process of engineers on-site-inspection involved. The robots also can gather the static data of the nonstructural elements from the sensor, which are distributed on the nonstructural elements. To demonstrate the effectiveness of the inspection robot, the robot is utilized to estimate the ceiling of a real structure damaged by the 2011 off the Pacific coast of Tohoku Earthquake. And conceptual experiment is also conducted for the purpose of evaluating the proposed damage assessment methodology in cooperation with the smart sensor and the inspection robot. The proposed methodology will provide useful information to the maintenance and repair planning of a damaged structure.

Abstract: This paper presents an overview of a set of tests performed by Embraer with two different SHM technologies in an E-Jets flight tests aircraft. Considered as promising technologies for monitoring structural parts, sensors networks including cables and connectors of CVM (Comparative Vacuum Monitoring) and LW (Lamb Waves) were installed in an Embraer-190 aircraft. The two technologies have been investigated by Embraer within the companys effort on Structural Health Monitoring. Scheduled maintenance and inspection activities can take advantage of the SHM technologies by evaluating the structural integrity of an aircraft with on-board sensors and performing less time-consuming procedures compared to current NDT technologies which can not only reduce the amount of time and burden of those activities, but also minimize the effects of human-factors when compared to current inspection tasks. The tests performed with CVM and LW components (sensors, connectors and cables) installed in a flight tests aircraft focus on the investigation of the technologies capabilities of withstanding the real aircraft operational conditions. Periodic monitoring of these on-board sensors has been performed using CVM and LW ground equipments. A further phase of this project is currently under development and focus on the demonstration of an on-board in-flight version of the CVM instrumentation system for continuous monitoring of aircraft structures during flight, aiming to demonstrate the ability of the CVM on-board equipment to withstand the aircraft in-flight environmental and operational conditions. Preliminary results on both partially and totally on-board equipments indicate that they can withstand the environmental and operational conditions; however, further tests need to be performed. Performing periodic inspections on ground with SHM systems lead to different qualification requirements when compared to those required for a complete on-board system that performs continuous monitoring. An overview of those two aspects of qualification requirements will also be presented.

Abstract: Structural health monitoring refers to the process of making an assessment, based on nondestructive, in-situ, autonomous measurements, about the ability of a structure to perform its intended function. This paper presents work done on a bolted connection in carbon-fiber reinforced polymer composite materials. A composite specimen is bolted in a double lap joint configuration to a test apparatus that applies an increasing tensile load. Ultimately, the load results in bearing failure of the material around the bolt hole. To monitor the progression of damage, macro fiber composite sensors are bonded in a circular array around the bolt hole. These sensors are then used to generate ultrasonic guided waves, a popular technique in nondestructive evaluation because of the favorable combination of propagation distance and sensitivity to damage. As the specimen is subjected to increasing load levels, measurements are taken repeatedly and compared with one another. Because damage will change the local mechanical properties of the material, the ultrasonic waves passing through the damaged region will be scattered differently in each direction, resulting in a different waveform arriving at the other surrounding sensors. By applying appropriate signal processing techniques, these changes may be interpreted as indicating the extent of damage that has occurred in the specimen. Preliminary analysis is presented demonstrating the correlation between changes in received strain signals and increasing damage levels.

Abstract: This paper presents an overview of the challenges an original equipment manufacturer (OEM) such EMBRAER may face to introduce scheduled structural health monitoring (S-SHM) applications in the maintenance programs of its commercial aviation aircraft models. S-SHM solutions have the potential to reduce aircraft operators direct maintenance costs and fleet downtime while keeping aircraft airworthiness at a minimum maintenance downtime and costs. As part of new approach in terms of scheduled maintenance practices, the replacement or complementation of traditional structural inspections tasks by new maintenance procedures taking credit of SHM technologies must be done in ways that meet the expectations and requirements of Regulatory Authorities, OEMs and airlines maintenance and engineering departments related to topics such as: safety, continued airworthiness, cost/benefits ratio, S-SHM systems built-in redundancies and reliability to support higher fleet availability, as well as necessary mechanics qualification. Besides the efforts for validation, verification, qualification and certification of such systems to deliver the expected effectiveness levels to verify structural integrity and withstanding the operational conditions to which it will be exposed, an OEM intended to offer their customers with the benefits of S-SHM solutions will be required initially to revise its policy and procedures handbooks (PPH) to adopt the new S-SHM Air Transport Associations Maintenance Steering Group 3 (MSG-3) Methodology guidelines. This will alter in different ways the current Maintenance Review Board processes conducted by each OEM to develop and revise the minimum scheduled maintenance program for a given commercial aircraft type certificate. The contents of the Maintenance Review Board Reports (MRB) will need to be revised in order to clearly indicate the scope and frequencies of each approved S-SHM task, and how they will replace, complement and/or be an alternative means of compliance of the more traditional maintenance tasks types such as general and detailed visual inspections (GVI and DET, respectively). Additionally, the Airplane Maintenance Manuals (AMM) will need to be revised to include specific S-SHM procedures on how to perform the intended inspection, how to proceed when degradation is detected in the monitored structures and how to repair such systems in case of failures.

Abstract: A beamforming array technique with four sensors is applied to a cylindrical geometry for detecting point of impact. A linear array of acoustic sensors attached to the plate record the waveforms of Lamb waves generated at the impact point with individual time delay. A beamforming technique in conjunction with an optimization scheme that incorporates the direction dependent guided Lamb wave speed in cylindrical plates is developed. The optimization is carried out using the experimentally obtained wave speed as a function of propagation direction. The maximum value in the beamforming plot corresponds to the predicted point of impact. The proposed technique is experimentally verified by comparing the predicted points with the exact points of impact on a cylindrical aluminum plate and a cylindrical composite shell. For randomly chosen points of impact the beamforming technique successfully predicts the location of the acoustic source.

Abstract: The paper investigates experimentally the effect of low-frequency vibration on nonlinear vibro-acoustic wave modulations applied to the detection of Barely Visible Impact Damage (BVID) in a composite plate. Finite Element (FE) modeling was used in a pretest stage to identify different motion scenarios of delaminated surfaces and relate them to natural frequencies of the damaged plate. In particular the opening-closing and frictional sliding actions of the defected interfaces have been considered. Subsequently, the identified frequencies have been used for low frequency excitation in nonlinear acoustic experiments on a composite plate with impact damage.

Abstract: The paper deals with practical aspects of Thermographic Nondestructive Testing (TNDT). A comparative study of burst vibrothermography (VT) and pulsed thermography (PT) measurements is presented and discussed. The authors have developed a diagnostic system for thermographic testing of structures that was used to perform experiments. Supported test modalities include burst vibrothermography and pulsed thermography, among other techniques. The system comprises both hardware and software components facilitating TNDT inspections. Experimental testing has been performed, on a composite plate, using the developed diagnostic system and two of the supported test modalities. The goal of these investigations was to compare the performance of both TNDT methods in revealing Barely Visible Impact Damage (BVID) in a composite plate.

Abstract: Boeing, CSIRO and DSTO are collaborating on research into Intelligent Health Monitoring for Aerospace Vehicles (IHMAV). The system has the ability both to predict the probable development of corrosion and to elucidate the environmental factors that are promoting corrosion. The paper discusses the system capabilities, data output including the data derived from previous monitoring programs on B-707. In particular this data established the connection between local microclimate and corrosion events and highlights variations in microclimate and corrosion that can occur for different spaces in an airframe and different airframes.

Abstract: This paper presents ongoing work by the authors to implement real-time structural health monitoring (SHM) systems for operational research-scale wind turbine blades. The authors have been investigating and assessing the performance of several techniques for SHM of wind turbine blades using piezoelectric active sensors. Following a series of laboratory vibration and fatigue tests, these techniques are being implemented using embedded systems developed by the authors. These embedded systems are being deployed on operating wind turbine platforms, including a 20-meter rotor diameter turbine, located in Bushland, TX, and a 4.5-meter rotor diameter turbine, located in Los Alamos, NM. The SHM approach includes measurements over multiple frequency ranges, in which diffuse ultrasonic waves are excited and recorded using an active sensing system, and the blades global ambient vibration response is recorded using a passive sensing system. These dual measurement types provide a means of correlating the effect of potential damage to changes in the global structural behavior of the blade. In order to provide a backdrop for the sensors and systems currently installed in the field, recent damage detection results for laboratory-based wind turbine blade experiments are reviewed. Our recent and ongoing experimental platforms for field tests are described, and experimental results from these field tests are presented. LA-UR-12-24691.

Abstract: With any structural health monitoring (SHM) system, verification of the health of the sensing elements is essential in ensuring confidence in the measurements furnished by the system. In particular, SHM systems utilised for structural hot spot monitoring applications will conceivably require transducers to operate reliably after sustained exposure to severe mechanical loading. Consequently, a good understanding of the long term mechanical durability performance of structurally integrated piezoelectric transducers is vital when designing and implementing robust SHM systems. An experimental facility has been developed at the Australian Defence Science and Technology Organisation (DSTO) capable of performing an autonomous long-term mechanical durability test on piezoceramic transducers. The Autonomous Mechanical Durability Experimentation and Analysis System (AMeDEAS) incorporates a general purpose data acquisition program controlling up to three 8-channel relay multiplexers and two instruments. AMeDEAS is highly flexible, allowing user-specified channel configurations and automatic interrogation of selected instruments. The system also interfaces with the uni-axial mechanical testing machine to provide control of the load sequence allowing transducer elements to be interrogated under stable load-free conditions after being subject to a predefined loading regime. AMeDEAS was used to investigate the fatigue characteristics of a low-profile layered piezoceramic transducer package developed by DSTO. A total of 16 transducers were tested under tension-dominated cyclic loading with peak-to-peak strain amplitude increasing from 400 με to a maximum of 3000 με, with periodic acoustic transduction efficiency and electromechanical impedance measurements taken throughout the test. This paper details the AMeDEAS and includes preliminary results which confirm the efficacy of the new facility.