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

In this paper we summarize the hardware and software issues of impedance-based structural health moni- toring based on piezoelectric materials. The basic concept of the method is to use high-frequency structural excitations to monitor the local area of a structure for changes in structural impedance that would indicate imminent damage. A brief overview of research work on experimental and theoretical stud- ies on various structures is considered and several research papers on these topics are cited. This paper concludes with a discussion of future research areas and path forward. Piezoelectric materials acting in the "direct" manner pro- duce an electrical charge when stressed mechanically. Con- versely, a mechanical strain is produced when an electrical field is applied. The direct piezoelectric effect has often been used in sensors such as piezoelectric accelerometers. With the converse effect, piezoelectric materials apply local- ized strains and directly influence the dynamic response of the structural elements when either embedded or surface bonded into a structure. Piezoelectric materials have been widely used in structural dynamics applications because they are lightweight, robust, inexpensive, and come in a variety of forms ranging from thin rectangular patches to complex shapes being used in microelectromechanical systems (MEMS) fabrications. The applications of piezoelectric mate- rials in structural dynamics are too numerous to mention and are detailed in the literature (Niezrecki et al., 2001; Chopra, 2002). The purpose of this paper is to explore the importance and effectiveness of impedance-based structural health mon- itoring from both hardware and software standpoints. Imped- ance-based structural health monitoring techniques have been developed as a promising tool for real-time structural dam- age assessment, and are considered as a new non-destructive evaluation (NDE) method. A key aspect of impedance-based structural health monitoring is the use of piezoceramic (PZT) materials as collocated sensors and actuators. The basis of this active sensing technology is the energy transfer between the actuator and its host mechanical system. It has been shown that the electrical impedance of the PZT material can be directly related to the mechanical impedance of a host structural component where the PZT patch is attached. Uti- lizing the same material for both actuation and sensing not only reduces the number of sensors and actuators, but also reduces the electrical wiring and associated hardware. Fur- thermore, the size and weight of the PZT patch are negligible compared to those of the host structures so that its attach- ment to the structure introduces no impact on dynamic char- acteristics of the structure. A typical deployment of a PZT on a structure being monitored is shown in Figure 1. The first part of this paper (Sections 2 and 3) deals with the theoretical background and design considerations of the impedance-based structural health monitoring. The signal processing of the impedance method is outlined in Section 4. In Section 5, experimental studies using the impedance approaches are summarized and related previous works are listed. Section 6 presents a brief comparison of the imped- ance method with other NDE approaches and, finally, sev- eral future issues are outlined in Section 7. 2. Theoretical Background

Overview of Piezoelectric Impedance-Based Health Monitoring and Path Forward

Medical applications of infrared thermography: A review.

The intensity of the infrared radiation emitted by objects is mainly a function of their temperature. In infrared thermography, this feature is used for multiple purposes: as a health indicator in medical applications, as a sign of malfunction in mechanical and electrical maintenance or as an indicator of heat loss in buildings. This paper presents a review of infrared thermography especially focused on two applications: temperature measurement and non-destructive testing, two of the main fields where infrared thermography-based sensors are used. A general introduction to infrared thermography and the common procedures for temperature measurement and non-destructive testing are presented. Furthermore, developments in these fields and recent advances are reviewed.

/pdf/infrared-thermography-for-temperature-measurement-and-non-2r2amijcr4.pdf

Infrared thermography for temperature measurement and non-destructive testing.

A review provided about non-destructive testing (NDT) methods for the evaluation of composites. The review considers the capabilities of most common methods in composite NDT applications such as Visual Testing (VT or VI), Ultrasonic Testing (UT), Thermography, Radiographic Testing (RT), Electromagnetic Testing (ET), Acoustic Emission (AE), and Shearography Testing with respect to advantages and disadvantages of these methods. Then, methods categorized based on their intrinsic characteristics and their applications.

https://cyberleninka.org/article/n/593997.pdf

A review of non-destructive testing methods of composite materials

A new method for determining the crystal orientation of [011] poled relaxor ferroelectric single crystal (RFSC) disks has been developed. This Technical Note describes the measurement techniques and mathematical approaches associated with this new method, which is possible due to the anisotropic response of [011] poled single crystal disks. Experimentally, the disks are subject to a distributed edge load at a series of angular orientations, with the output voltage recorded at each orientation. Equations have been developed to govern a particle swarm to find an optimised fit to the experimental data yielding the crystal orientation of the disk which is required for practical applications. Approximate values for the piezoelectric charge constants d 31, d 32 are also determined. The method is demonstrated on a RFSC Mn-PMN-PZ-PT disk, comparing favourably with a synchrotron x-ray transmission diffraction study on the same disk.

A method for determining the orientation of [011] poled relaxor ferroelectric single crystal disks

The concept of in situ Structural Health Monitoring (iSHM) involves incorporating a diagnostic capability to detect and monitor damage in structural ‘hot spots’. These systems allow the introduction of Condition Based Monitoring (CBM) approaches for ageing aircraft fleets and thus could help significantly reduce through-life support costs and increase aircraft availability. The Australian Defence Science and Technology Organisation (DSTO) has a program of work aimed at developing autonomous, robust, reliable iSHM systems with the specific aim of retro-fitment to existing aircraft. A current laboratory demonstrator of the technology is focused on the application of an acousto-ultrasonic (AU)-based iSHM system for monitoring fatigue cracks on generic structurally-detailed lower wing skin (LWS) panel specimens. This particular scenario, which simulates the LWS on an F-111C aircraft, is considered an ideal developmental platform and springboard for future iSHM applications, since it captures a number of key issues that AU-based iSHM systems need to address to ensure robust reliable diagnostics, viz., complex structural geometry, crack closure and high operational loads. This paper describes the design, application and assessment of an AU-based iSHM system to detect and monitor growth of fatigue cracking in the generic complexgeometry LWS panel specimens subject to representative spectrum loading. Its performance is discussed and compared to measurements furnished by thermoelastic stress analysis and visual observation. Testing associated with this complex realistic panel specimen revealed several deficiencies in the design of the iSHM system.

Acousto-Ultrasonic In Situ Monitoring of Fatigue Cracking in an Aircraft Wing Skin Specimen

Large sheets of high-density polyethene geomembrane are used as floating covers on some of the wastewater treatment lagoons at the Melbourne Water Corporation’s Western Treatment Plant. These covers provide an airtight seal for the anaerobic digestion of sewage and allow for harvesting the methane-rich biogas, which is then used to generate electricity. There is a potential for scum to develop under the covers during the anaerobic digestion of the raw sewage by microorganisms. Due to the nature of the operating environment of the lagoons and the vast size (450 m × 170 m) of these covers, a safe non-contact method to monitor the development and movement of the scum is preferred. This paper explores the potential of using a new thermographic approach to identify and monitor the scum under the covers. The approach exploits naturally occurring variations in solar intensity as a trigger for generating a transient thermal response that is then fitted to an exponential decay law to determine a cooling constant. This approach is investigated experimentally using a laboratory-scale test rig. A finite element (FE) model is constructed and shown to reliably predict the experimentally observed thermal transients and cooling constants. This FE model is then set up to simulate progressive scum accumulation with time, using a specified scumberg geometry and a stepwise change in thermal properties. The results indicate a detectable change in the cooling constant at different locations on the cover, thereby providing a quantitative basis for characterising the scum accumulation beneath the cover. The practical application and limitations of these results are briefly discussed.

Thermographic Monitoring of Scum Accumulation beneath Floating Covers

Detection of disbonds in scarf joints using Lamb waves

Military and civilian aircraft operators are constantly striving to reduce sustainment costs while maintaining and/or improving aircraft availability and safety. These goals, which on the surface may appear contradictory, can be achieved through the introduction of structural health monitoring systems. The paper describes an Australian perspective on the development, validation, certification and implementation of SHM systems toward technology demonstrators, in the context of approaches that meet Australian Defence Force aircraft structural integrity future requirements. doi: 10.12783/SHM2015/19

Nik Rajic

Papers

A method for determining the orientation of [011] poled relaxor ferroelectric single crystal disks

Acousto-Ultrasonic In Situ Monitoring of Fatigue Cracking in an Aircraft Wing Skin Specimen

Thermographic Monitoring of Scum Accumulation beneath Floating Covers

Detection of disbonds in scarf joints using Lamb waves

SHM Certification Requirements for Military Aircraft—An Australian Perspective